Canon EOS Rebel T4i DSLR

Canon EOS Rebel T4i DSLR

Recently, Canon released EOS Rebel T4i DSLR, its most sophisticated Rebel model. To the user, T4i model delivers amazing image quality with high performance, fast and intuitive operation. The innovative DIGIC 5 image processor stands behind most of the features of T4i at affordable price. You see below a picture of DIGIC 5 processor.

We will review briefly the several features made possible by DIGIC 5 processor:

High speed continuous shooting, able for recording at 5fps with the proven quality 18.0 Megapixel CMOS APS-C image sensor. For more on APS-C sensors, visit “Featured Lenses For Digital SLR Cameras” article

Improved autofocus performance using new autofocus (AF) sensor with a new 9-point, all cross-type AF system (including high-precision dual-cross f/2.8 center point). This system provides accurate focus whether the camera is oriented in portrait or landscape position and maintains consistent focus with an exceptional degree of reliability. Canon’s new Hybrid CMOS AF System is perfect for shooting photos and video in Live View. This new AF system combines two distinct AF technologies, such as phase and contrast detection AF, for speedier and more accurate focus. These complementary focusing systems are combined with signals from pixels on the camera’s CMOS sensor that assist in predicting subject location. Using prediction, continuous focus is tracking the moving subject quick and accurate in video recording while enhancing focusing speed. Below you see the position of focusing points as they appear when you look through the viewfinder.

14-bit A/Dconversion, which gives very natural color gradation, revealing fine color details. This features also allows shooting within broader sensibility range ISO100-12800; expandable to ISO25600 (H), from bright to dim light. For more explanation on exposure, please read the article Exposure in Digital Photography – Basics.

Enhanced Full HD Movie when selecting Movie Servo AF mode.

Posted in Digital SLRs

Camera Positioning

Camera Positioning in Video Surveillance Systems

This article gives several hints on positioning cameras of video surveillance system. Camera positioning is the key point of any video surveillance system. Any property has several key zones for monitoring such as entry and exit points, doors, windows and access ways to various facilities, to mention just a few of them. In the schematic Outdoor Surveillance below, you see an example of positioning two cameras for monitoring the pathway to the house and also the entrance to the house.

We bring to your attention the positioning of one or more cameras for obtaining the most relevant information on intruder such as face, size and eventually other particular features that will further help to its finding. A good suggestion is for using color cameras instead of black and white cameras. Skin color, eyes color and sometimes cloths colors might help a lot in identifying a person. In several situations such as video surveillance of babies, small children, and also in small businesses, audio recording can be very useful, too. Some comments on parameters of video surveillance cameras shown in the Surveillance Camera Positioning schematic can be helpful.

The lens of most video surveillance cameras has 3.6mm focal length and 67 degrees view angle. The camera can see clear images without adjusting the lens, from 2m away from the lens up to infinity. For 3.6mm lens, Camera Distance to Scene table shows horizontal dimension DH and vertical dimension DV of the scene for several values of Distance between the camera and the scene. Use this table for evaluation purposes only, to estimate where you should place the cameras. This table helps you also for positioning multiple surveillance cameras. However, for final positioning of each camera, you must use the camera image displayed by the surveillance system monitor.

Sometimes you must do surveillance of a wide scene, such as shown in Multiple Cameras Layout schematic. In this case, the surveillance must cover an area much wider than a single camera can handle. Obviously, you must use multiple cameras with reasonable overlap of their viewing scenes. Avoid gaps between

the viewed scenes for having the full coverage of the area under surveillance.

You must be aware to not mount the camera at more than 10m or 30ft from the scene. Most of surveillance cameras such as Foscam FI8910W Pan

& Tilt IP/Network Camera have 640×480 pixels (300k pixels over entire image). This pixel count does not provide clear enough pictures for objects located at more than 10m or 30ft away from camera. For objects located up to this distance, the pictures have reasonable clarity, as you can

see below in Mounting Wireless Surveillance Camera schematic.

Mount your camera as shown in the diagram above pointing to the door, but avoid targeting a bright background. If the camera targets a bright scene such as a window, as shown below in Camera and Light Sources schematic in the right hand side, is difficult to identify the intruder face. Obviously, this is not the purpose. The best position for the camera is with the window behind, such as shown in the schematic below, on the left hand side. However, the camera must avoid

targeting the bright sources.

Surveillance cameras have infra red LEDs for illuminating the scene in total darkness to the human eye. Video recordings in total darkness do not not have the same clarity as the scenes recorded in visible light. However, they give a good idea about the human faces, as you see in the Surveillance in Total Darkness schematic below. Ideally, the camera must be positioned at a convenient height, for having a good record of human faces. Very often, the thieves wear either a hood or a baseball cap, for making their face hard to identify.

We hope that this article provided you some useful tips for installing yourself the surveillance cameras at home and also at your small business.

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Posted in Video Surveillance

Surveillance System – Do It Yourself

Video Surveillance System – Do It Yourself

For multiple reasons, video surveillance systems are increasingly popular for home and small business, which is also the target of digihut.org. Therefore, we bring to your attention several security aspects related to home and small business.

A typical scenario for a security company chasing a new client looks like this:

A sales person comes with a “very good deal”, offering for free a $1,200 value surveillance system including installation, if you accept a 3-years monitoring contract with them, for $40.00/month.
Important to mention: the offer is for a typical security system with central unit, three door contacts, one motion sensor and one smoke sensor.

The math is quite simple: you must pay $480/year, or $1,400 over three years. Apparently, this does not look too bad: if you take for granted $1,200 the price of security system as they claim, for $200 extra you have the system installed by a technician in about 40 minutes, or you pay $300/hour installation fee!
Let’s look further on the surveillance job of the security company. Practically they do nothing until appears an alarm signal from the client, when they check if there is a true signal or not. If it appears to be a true alarm, they try to reach you by phone, to inform you about an intrusion attempt, or about a fire alarm. If you are not reachable, the surveillance company calls the Police. If the Police comes on place and there is no sign of intrusion and if this happens the first time, you get only a warning for a false alarm. If the surveillance company calls the Police again after a while and the Police finds again a false alarm, they will charge you this time! You cannot dispute with the security company; they always claim a perfect system, no glitches whatsoever. If you still insist that it was a glitch in the surveillance system, they will send you a technician on spot to fix the problem, but they will charge you for this. Usually, the field technicians have low expertise and they end up by doing something wrong in your system, which will create you problems later. Again, you cannot prove the technician’s expertise level. You are at the total mercy of the security company. You could break the contract, but you will be charged for this, according to the contract terms. This scenario is not hypothetical. It happened to us several times, turning our belief in a security company into a nightmare, with a lot of money loss.
 
Fortunately, technical progress in multiple domains such as image capture and storage, wireless communications, Internet and cellular telephony to name just a few of them, make property surveillance much more reliable and more affordable than it was until several years ago. The schematic Basic DIY 24/7 Video Monitoring shows how simple is to do yourself a 24/7 video surveillance system, monitored by yourself.

The key piece of your video surveillance is Foscam FI8910W Pan & Tilt IP/Network Camera with Two-Way Audio and Night Vision which is an integrated unit with high quality color video camera and microphone, infra-red – IR LED for illumination in the dark, pan/tilt function for improved exploration, embedded IR-cut filter and video recording system. The unit can be wirelessly connected to a local area network and further to Internet. However, Internet is increasingly popular and most likely you already have local wireless Internet installed and running. Up to four such cameras can be connected to the same wireless router. Any computer, tablet and smartphone (iPhone, Android and BlackBerry) can be connected to cameras if you provide their addresses. Foscam camera has an IR-Cut filter for enhanced color picture quality. You have two-way audio, 300 degrees pan and 120 degrees tilt, motion detection with email notification and image upload via FTP. You can do video and audio remote monitoring from anywhere in the world where is Internet connection.

Foscam Blue Iris Professional software supports several IP camera brands including Foscam and Agasio, has motion detection across a custom defined zone, H.264 video compression recording, e-mail and SMS text messaging alerts.

We recommend Medialink – Wireless N Broadband Router – 150 Mbps – 2.4GHz – 802.11n with Internal Antenna for your local area network – LAN, if you do not have already other router. However we keep posted this router on our list

of devices for DIY surveillance system.

You must protect your surveillance system against either intentional or involuntary power failure with CyberPower CP1500AVRLCD Intelligent LCD 1500VA 900W with AVR Tower UPS, which can be used also for powering your computer and your wireless router.

We do not include in our list the smartphone, which we suppose you already have. This is more and more a commodity in these days and also in the immediate future. Using a $3.99 application IP Cam Viewer for Android tablet, iPad, Droid 2 and Droid 3 phones, you can listen, control and record your camera from anywhere in the world with Internet connection.

Let us summarize our recommendations for using DIY remote video monitoring over Internet. Continuously decreasing prices of components for security systems prevent us to give you even a short term price. We can provide estimates only. For current prices, visit the links provided.
DIY Option A: You need a single Foscam FI8910W camera. You have the wireless router, backup power supply, and the smartphone. Your investment is below $99.99.

DIY Option B: You need four Foscam FI8910W cameras and also Foscam Blue Iris Professional software. You suppose to have the wireless router, backup power supply, and the smartphone. Your investment is below $448.

DIY Option C: Option B , where you must buy the backup power supply for less than $150. Your investment is below $598.

Now, you compare DIY Options A, B and C with:

Security company: $1,400.00 for three years, or $467.00/year and hassle. It is up to you to make comments and to decide which way to go.

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Posted in Video Surveillance

Featured Lenses

Featured Lenses For Digital SLR Cameras

The progress of digital SLR cameras is credited mainly to three main elements: lens, image sensor and digital image processor. At digihut.org, we have more than 1,400 digital SLR cameras for you to choose from. Selection of digital SLR camera is an important investment in your passion, which eventually could turn into a a very serious business. The selection of digital SLR camera is subject of many criteria, technical and personal. We do not touch the personal criteria; they are out of any discussion. In this article we use our professional expertise to bring into discussion several characteristics of featured lenses such as Image Stabilization – IS and Tilt Shift – TS. We intend to help users to make better pictures by the explaining the operation of these advanced lenses. We strongly recommend you to consider this article as an incentive for reading more on the topics below and also for discussions and practising on this subject. First, we review some parameters frequently advertised for digital SLR cameras and also related to featured lenses.
 
Number of pixels such as 18MP and 22.3MP are frequently used for advertising digital SLR cameras. This is an important parameter contributing to the picture quality, but components such as signal processor, light metering system, image focusing are very important, too. We explain below the connection between the number of pixels of digital SLR camera, their lenses and picture quality. Each digital SLR camera manufacturer has lenses compatible with its cameras. Lens compatibility covers not only the mount, but also optical parameters and electrical compatibility with the camera body, including the operation of entire lens. It is a very strong operational link between digital SLR camera and the lens attached to it. If you do not use the lens for recommended camera models, some features of the lens might not work, even if the lens and digital SLR camera come from the same manufacturer.
 
Camera format such as APS-C and Full Frame refers to the sensor type. Cropped Images schematic shows three very popular Canon image sensors and their dimensions.
Full Frame sensor size has the advantage of larger field of view of lenses designed for this format. The drawbacks are large size of camera body and also of lenses designed for Full Frame format. APS-C sensors have some advantages for telephoto, such as smaller size and lighter cameras than Full Frame digital SLR cameras. Also the lenses designed for APS-C sensors are smaller and lighter than the lenses designed for Full Frame sensor. It is easy to understand that when goes into optimization, both camera and its lenses are built around the image sensor. Further you will see some aspects.
 

Some comments on sensor format, number of pixels, pixel area and pixel size for Canon and Nikon brands clarify several aspects, directly applicable to other brands, too.
 

Canon APS-C sensor format has 22.2mmX14.8mm, or 329sq-mm [square-millimeters] area. For 18MP count such as in Canon EOS Rebel T3i 18MP CMOS Digital SLR Camera, pixel area is 18.3sq-microns [square-microns], or about 4.3micronsX4.3microns size [1micron = 0.001mm]. Canon EOS 5D Mark III 22.3MP Full Frame Camera has Full Frame sensor of 36mmX24mm size, or 864sq-mm, which is 2.63 times larger than APS-C sensor area. With its 22.3MP total count, single pixel area is 38.74sq-microns or about 6.2micronsX6.2microns size, which is 2.11 times larger than the pixel area of APS-C sensor. From comparison of these digital SLR camera types, we notice several aspects:

(i) For Canon digital SLR cameras, one pixel of Full Frame sensor is about two times larger than one pixel of APS-C sensor and obviously captures about two times more light. Therefore, Full Frame sensor is twice more sensitive to light than APS-C sensor, which is good for low-light exposure.

(ii) In all digital cameras, each pixel takes a sample of the image across its area. Entire picture is no more than a collection of samples taken by each pixel. Higher pixel count per unit area, or pixel density, gives more detailed or sharper image than lower pixel density. In our cases, 22.3MP Full Frame sensor has 0.026MP/sq-mm, and 18MP APS-C sensor has 0.055MP/sq-mm. If the appropriate lens is used for each sensor, the math is quite simple. Full Frame sensor area is 2.63 times larger and pixel size is 2.11 times larger than APS-C sensor. There is no significant difference in image sharpness between APS-C cameras and Full Frame cameras. Full Frame cameras have larger Field Of View or FOV, as you see in DX and FX Cameras with Lenses diagram.
Large FOV is the reason for using Canon EOS 5D Mark II 21.1MP Full Frame CMOS Digital SLR Camera for replacing the usual 35mm film format for shooting movies.
We notice that Nikon DX cameras give slightly less sharp pictures, have lower light sensitivity and smaller size and weight than Nikon FX cameras. You can overcome light sensitivity issue by using a tripod, which however must be used for sharp picture when shooting in low light at ISO100 speed. Large FOV is the main advantage of Full Frame digital SLR, not considering other operational features such as 39-points autofocus system versus 11-points autofocus encountered in DX format cameras.

(iii) Several lenses such as Canon EF-S 55-250mm f/4.0-5.6 IS II Telephoto Zoom Lens for Canon Digital SLR Cameras, are optimized for image projection on entire surface of APS-C sensor with crop factor close to one. If you use Canon EF 75-300mm f/4-5.6 III Telephoto Zoom Lens for Canon SLR Cameras optimized for Full Frame sensor on camera with APS-C sensor, the image will be cropped with 1.6 factor in its central part, as you see in the Cropped Images schematic. However, across its area, APS-C cropped picture will reveal more details than the picture taken with the same Full Frame lens mounted on Full Frame camera. In the schematic below, you can compare the blurred picture with sharp picture. Be aware that blur was exaggerated on purpose, for highlighting the difference in sharpness. Spatial resolution is the professional term used for image sharpness: high spatial resolution reveals more details than low spatial resolution.
 

Nikon DX sensor has 23.6mmX15.8mm size, or 372.88sq-mm area. For its 24.2MP count such as in Nikon D3200 24.2MP CMOS Digital SLR, pixel area is 15.4sq-microns, and pixels density is 0.065MP/sq-mm. With Nikon 55-200mm f/4-5.6G ED IF AF-S DX VR Nikkor Zoom Lens optimized for DX sensor, crop factor does not limit the picture size. The FX sensor of Nikon D800E 36.3MP CMOS FX-Format Digital SLR Camera has 36mmX23.9mm size with total area of 860.4sq-mm and pixels density of 0.042MP/sq-mm. Using DX sensor as reference, FX sensor pixel area is 1.5 times larger than the area of DX pixel with total area 2.3 larger than of DX total area. Looking at these numbers, for FX sensor we see 1.5 decrease in picture sharpness, but 2.3 time increase in light sensitivity. Not counting additional features of FX cameras, DX cameras give better picture sharpness with less light sensitivity than FX cameras. Using ISO100 and tripod for sharp picture, light sensitivity can be compensated by longer exposure or slower shutter speed. With Nikon 35mm f/1.4G AF-S FX SWM Nikkor Lens for DSLR Cameras optimized for FX sensor, Nikon D800E DSLR will reveal theoretically finer details than Canon EOS 5D Mark III 22.3MP Full Frame camera with Full Frame working with Canon EF 75-300mm f/4-5.6 III Telephoto Zoom Lens. The picture file released by digital camera is subject to very complicate computations made by its digital image processor, which can affect the details of the final picture.

DX and FX Cameras with Lenses schematic shows the fields of view of each FX and DX Nikon cameras working with their optimized lenses. DX configuration has a narrower field of view or FOV than FX configuration. Nikon D3200 24.2MP CMOS Digital SLR with FX optimized lens will crop the central part of the image with 1.5 crop factor, showing slightly finer details than the image of the same object taken with DX optimized lens.
 

Modulation Transfer Function (MTF) is a measure of optical quality of a lens. MTF plots contrast and resolution graphs of the lens staring from center toward its boundary referenced to a “perfect” lens that transmits 100% of the light and reveals the image with infinitely small details. Of course, the perfect lens does not exist; it is just a theoretical reference. Any MTF plot shows on horizontal axis X the distance from lens center toward its boundary, in millimeters. The vertical axis Y shows the transmission from zero (no transmission) to 1 (100% transmission). MTF plots are traced along two conventional lines or directions such as Sagittal and Meridional, for two spatial frequencies defined by two group of lines:

(sf1) Low spatial frequency MTF plot for 10lines/mm (100microns center to center line spacing) pattern shows lens contrast.

(sf2) High spatial frequency MTF plot for 30lines/mm (33.33microns center to center line spacing) pattern shows lens resolution or sharpness.

The schematic Sagittal and Meridional Lines below gives you better perception about both line groups and also about how sagittal and meridional lines are defined.

For Canon APS-C image sensor with 18MP, there are about 23pixels within 100microns line spacing (10lines/mm) and 7.75pixels within 33.33microns line spacing (30lines/mm). These pixels sample the image on image sensor above the Nyquist rate required for minimum recovery of the original image from sampled picture. As general rule, more pixels of the image sensor get sharper image.
 
Below you see two MTF examples for Canon EF-S 55-250mm f/4.0-5.6 IS II Telephoto Zoom Lens for Canon Digital SLR Cameras.


How can we read the above MTF diagrams? The graphs are for a zoom lens working between F=55mm and F=250mm. Accordingly, the diagrams are for both focal distances F=55mm of MTF Canon EF-S 55-250mm f/4-5.6 IS II and F=250mm of MTF Canon EF-S 55-250mm f/4-5.6 IS II. Canon MTF Charts have specific meanings such as:

(a) Thick lines are for 10lines/mm, and thin lines are for 30 lines/mm.
(b) Black lines are for maximum aperture f/5.6 and blue lines are for f/8.
(c) Solid lines on the graphs are for meridional direction of the image.
(d) Dashed lines in the graphs are for sagittal direction of the image.
(e) The difference between sagittal and meridional graphs comes from lens astigmatism.

Conclusions from the MTF graphs:

F=55mm

(c1) The contrast is almost constant across the entire lens aperture for f/5.6 diaphragm, on both meridional and sagittal directions. On sagittal direction, for f/8, contrast drops monotonically toward 70% by the lens boundary.

(c2) The image resolution or sharpness has little change across both meridian directions for both f/5.6 and f/8 diaphragms. On sagittal direction, sharpness has its maximum value in the central region of the lens up to 3mm radius, then decreases monotonically toward 40% by the lens boundary for both f/5.6 and f/8.0 diaphragms.

F=250mm

(c3) The contrast is almost constant for f/8.0 on meridional direction and has a small drop on sagittal direction over more than 10mm radius. It is also almost constant across the entire aperture for f/5.6 on meridional directions.

(c4) The sharpness has a drastic decrease for f/5.6 over 10mm radius, on both sagittal and meridional directions. For f/8 on meridional direction is a 15% decrease from center to boundary, but for f/5.6 there is a steep decrease toward 30% on both meridional and sagittal directions. This lens gives a blurred image toward its boundaries. Do not worry about this; it is very hard to notice that blur when reading the image at 100% magnification. You may notice some blur in picture over 150% magnification.
 
Lens contrast is linked to its resolution: when resolution decreases, contrast decreases, too; it is physics behind.
 

We show below also MTF plots for Nikon 55-200mm f/4-5.6G ED IF AF-S DX VR Nikkor Zoom lens, equivalent to the previous Canon lens.
 


 

Nikon provides MTF graphs with all notes for minimum (Wide) and maximum (Tele) focal distances. These plots show the overall lens behavior for Wide or F=55mm focal length and for Tele or F=200mm focal length.
 
There is no widely accepted standard for lens testing and for producing MTF graphs. Each lens manufacturer has its own procedures. Therefore, it is difficult to compare lenses with apparently similar focal distances and f/number from different manufacturers. However, the lens always works with the image sensor and with digital image controller. Ultimately, all these three elements must be considered together, or in other words, the picture is important.

Conclusions on lens optical quality:

(LQ1) Check to see if lens manufacturer provides MTF graphs, which is a proof that the lens should be made under tight quality control.

(LQ2) Select a lens with flat MTF graphs across maximum possible extent.

(LQ3) Final and the best check: look at the sample pictures made with your selected lens posted in your preferred sites dedicated to pictures, such as Amazon.com.

We recommend several popular lenses. Each link below directs you not only to the lens, but also to a multitude of shots made with that lens.


 

Image stabilization

Every type of lens brings its contribution to the image. This explains the large variety of available lenses compatible with practically all models of digital SLR camera from the same manufacturer such as Canon, Nikon, Sony, Olympus and Panasonic.
 
There are two types of subjects: static and moving, and also two ways of shooting: handheld and using tripod. In all the above discussions, we assumed shooting static subjects with camera locked on rigid tripod. Very often, several amateurs and professional photographers shoot static subjects with tripod and at low speed such as ISO100 or ISO200 for the best picture sharpness. Assuming a perfect focus in handheld shooting, the camera always moves slightly during the exposure; the only question is how much it moves. If the camera moves within the sharpness limits of the lens not detected by the image sensor, you do not see any blur in the picture. If the camera moves beyond the sharpness limits detected by the image sensor, the picture appears blurred more or less. The photographers use various approaches to get sharp pictures when shooting with handheld camera:

(sh1) Increase sensitivity of camera beyond ISO200. According to camera specifications, you can shoot pictures with correct exposure up to ISO6400 or more. Be aware that at high ISO_speed, the picture also gets blurred because of image sensor noise. Higher ISO_speed gives more noise in the picture.

(sh2) Faster shutter speed below 1/125 will get a reasonable sharp picture with handheld shooting: the camera freezes the scene. It is expected a blurred image when shutter speed is slower than f/[focal length]. This empirical rule shows that shooting with telephoto lenses are likely to blur the image for handheld shooting, unless the image move is mitigated up to the point where the camera autofocus can work properly.

(sh3) Use larger diaphragm or iris, to get more light on the image sensor. Be aware that the diaphragm number controls the depth of field – DOF of the lens. As an example, when using f/4 diaphragm you have shorter DOF than when using f/8 diaphragm; therefore when adjusting the diaphragm you are playing also with the depth limits of image sharpness.
 

Image Stabilization (IS) feature mitigates the image shake on image sensor, thus allowing stable image up to four stops slower. This is a tremendous advantage versus the regular lenses without IS, especially when shooting in darker ambient light.

The schematic Canon Conventional IS – OFF shows two arbitrary situations encountered in normal operation when using regular lenses for shooting, or when using a lens with IS feature disabled. This schematic shows a simulated shake for better understanding of the real case when using telephoto lenses. You notice the difference in scene positions between the two instances when the scene moves too much and too fast, which prevents the lens to keep focusing on the scene.
 

The schematic Camera Shake below explains compensation of camera movement during shooting.
 

When shooting either a static or a slow-moving scene, camera shaking in arbitrary way can be decomposed in tilt and shift shakes as shown in Camera Shake schematic above. Any tilt has a horizontal component or yaw and also a vertical component or pitch as figured out by the arrow pairs. Accordingly, there is an angular velocity sensor for each shake component. Angular tilt of the camera lens produces an image shift on the image sensor. Camera processor uses the signals from these two angular velocity sensors for shifting the Image Stabilizer perpendicular on optical axis. Tilt Compensation schematic below shows how conventional IS works. You can see also the look of some Canon IS units.
 

Select IS ON button in the link below to see IS lens moving and also mitigation of image shake.

IS operation is simple: when the lens tilts downwards, the image projected by the lens on the image sensor shifts. The Image Stabilizer Unit within the lens shifts its Image Stabilizer Lens perpendicular to the optical axis according to signals provided by both angular velocity sensors. It is obvious that the Image Stabilizer Lens moves simultaneously in two directions within a plane perpendicular on the optical axis. This reduces significantly the image shift on the image sensor up to the equivalent of four stops slower. This classical image stabilization has different brand names. Canon calls it Image Stabilization IS Mode 1 and Nikon calls it Vibration Reduction VR. It is really great help for many situations. Of course, IS or VR feature can be enabled and disabled anytime by the user. It is obvious that there is a time constant associated to this image stabilization, which limits the image stabilization to relatively slow shaking.

WARNING: Long focal length is likely to produce blur with classical lens even when shooting at 1/125 or less. Image stabilization does not work if the image shakes too fast. When shooting with IS enabled, be careful to stay within maximum four stops slower than when IS is disabled.

The schematics below show two situations of aiming the scene with IS disabled and enabled. It is easy to notice how small is the image shift on image sensor surface with IS enabled.
 
Click ON button in the image provided by the link below to see image stabilization.

In the above example, notice that Canon IS I works better on the swimmer than on the water waves and drops, which move faster than the swimmer. This example is in good agreement with the above warning for image stabilization effective on slow-moving scenes.
 

When panning camera on a moving subject such as shown in Canon Image Stabilization IS-Mode 2 Panning schematic, IS operation may interfere with subject background. Both the subject and the background are moving.
In horizontal panning, the photographer follows the subject horizontally. The subject moves slower than the background, with sudden changes in its positions towards the frame. In this case, IS must compensate only for vertical changes. The background appears blurred.

In vertical panning, IS must compensate only for horizontal changes. Canon names IS Mode 2, image stabilization on panning.

The schematic below shows Canon EF 70-300mm f/4-5.6 IS USM Lens for Canon EOS SLR Cameras with the operating instructions for selecting IS 1 and IS 2 modes of operation.
 

We recommend below several Canon lenses with IS feature. For the entire range of Canon IS lenses, visit the link Canon Image Stabilization Lenses.

(ISL1) Canon EF-S 55-250mm f/4.0-5.6 IS II Telephoto Zoom Lens for Canon Digital SLR Cameras

(ISL2) Canon EF 75-300mm f/4-5.6 III Telephoto Zoom Lens for Canon SLR Cameras

(ISL3) Canon EF 70-300mm f/4-5.6 IS USM Lens for Canon EOS SLR Cameras

(ISL4) Canon EF 75-300mm f/4-5.6 III USM Telephoto Zoom Lens for Canon SLR Cameras

(ISL5) Canon EF 70-300mm f/4-5.6 IS USM Lens for Canon EOS SLR Cameras

(ISL6) Canon EF 28-135mm f/3.5-5.6 IS USM Standard Zoom Lens for Canon SLR Cameras

(ISL7) Canon EF 24-105mm f/4 L IS USM Lens for Canon EOS SLR Cameras.
 

Several Canon lenses have IS Mode 3 feature which stabilizes the image only when the shutter is fully pressed. IS Mode 3 is recommended for fast acting scenes, such as sport subjects. IS Mode 3 is an extension of IS Mode 2, which stabilizes the image on direction perpendicular to panning. We recommend to visit Canon EF 300mm f/2.8L IS USM II Super Telephoto Lens for some additional information.

We recommend several Canon lenses with IS Mode 3, such as:

(ISL8) Canon EF 300mm f/2.8L IS USM II Super Telephoto Lens for Canon EOS SLR Cameras

(ISL9) Canon EF 400mm f/2.8L IS USM II Super Telephoto Lens for Canon EOS SLR Cameras

(ISL10) Canon EF 500mm f/4L IS II USM Lens

(ISL11) Canon EF 600mm f/4L IS II USM Lens.
 
Hybrid Image Stabilization works on both tilt shake and shift shake. This feature is encountered at Canon EF 100mm f/2.8L IS USM Macro Lens for Canon Digital SLR Cameras. The schematic below shows the lens and its stabilization features.

Dynamic IS feature added on top of IS feature keeps image sharpness when the subject moves either toward camera or in opposite direction, shown as Axial Shake in Camera Shake schematic. Canon EF-S 18-135mm f/3.5-5.6 IS STM has Dynamic IS feature, very useful for video shooting. Below you have an image of this lens.

 
Nikon Vibration Reduction – VR technology uses the same principle as Canon Image Stabilization – IS technology, explained in Tilt Compensation Schematic. As you see in this schematic, Vibration Reduction Units and Image Stabilization Units look similar, but of course there are different, built according to each manufacturer’s design for digital cameras and their lenses. VR II option operates faster than VR option.

For panning, VR detects camera movement and automatically suppresses the blur-correction function. If the camera shakes horizontally, VR reduces blur in the vertical direction. With this function, the panning effect is maximized. Panning Detection is effective regardless of the camera’s orientation or direction of motion, either horizontal or vertical.
A schematic of Nikon 18-200mm f/3.5-5.6G AF-S ED VR II Nikkor Telephoto Zoom Lens for Nikon DX-Format Digital SLR Cameras and a schematic of Vibration Reduction features of VR and VR II models are shown below.
 

We recommend below several popular models of Nikon lenses with VR features, from the top list of our Nikon lenses collection. For our entire VR collection, visit Nikon VR lenses for Nikon digital cameras.

(VR1) Nikon 55-200mm f/4-5.6G ED IF AF-S DX VR [Vibration Reduction] Nikkor Zoom Lens

(VR2) Nikon 70-300mm f/4.5-5.6G ED IF AF-S VR Nikkor Zoom Lens for Nikon Digital SLR Cameras

(VR3) Nikon 55-300mm f/4.5-5.6G ED VR AF-S DX Nikkor Zoom Lens for Nikon Digital SLR

(VR4) Nikon 18-200mm f/3.5-5.6G AF-S ED VR II Nikkor Telephoto Zoom Lens for Nikon DX-Format Digital SLR Cameras

(VR5) Nikon 105mm f/2.8G ED-IF AF-S VR Micro-Nikkor Lens

(VR6) Nikon 28-300mm f/3.5-5.6G ED VR AF-S Nikkor Zoom Lens for Nikon Digital SLR

You see sample images with Nikon VR disabled (OFF) and enabled (ON).

 

Tilt Shift – TS Lenses

In the schematic Perspective Correction with TS Lens the same building was shot from the same position with a regular wide angle lens (left hand side) and with TS lens (right hand side). The picture on the left has the inherent geometric distortions of the wide angle lens when shooting relatively close to subject. Skilled photographers use sometimes these distortions for producing special effects.

When you want the building to appear straight all the way up, the use of Tilt Shift – TS lens is required. The operation of TS lens is based on Scheimpflug principle shown in the schematic Tilt For Focus on Oblique Subjects below.

Scheimpflug discovered more than 100 years ago that you can get sharp images with very large Depth Of Field for subjects making an acute angle with the image senor (in our case), if you tilt the lens in such a way that the subject plane, the lens plane and the image sensor plane all meet along the same Hinge Line, followed by a lens shift to make the image on the sensor. The schematic Tilt For Focus on Oblique Subjects shows the Hinge Point, which is the intersection between the Hinge Line and the plane of schematic.
Practically, with TS lenses you make perspective corrections in two steps:
First, tilt the lens for focusing on subject.
Next, shift the lens until you get the best perspective correction, as in the diagram below.
If necessary, make another iteration until you get the best image, then shoot.

Electro-Magnetic Diaphragm – EMD module of canon works in tandem with electronic lens system for providing accurate control of light flux on the image sensor and almost circular aperture shape. The schematic Canon EMD below shows simulated extreme positions of diaphragm.

Below you see a picture of Canon TS-E 17mm f/4L UD Aspherical Ultra Wide Tilt-Shift Lens for Canon Digital SLR Cameras.

You can have access to our entire Canon TS lenses collection by visiting the link Canon Tilt Shift Lenses. We recommend below from the most popular models:

(CTSL 1) Canon TS-E 24mm f/3.5L II Ultra Wide Tilt-Shift Lens for Canon Digital SLR Cameras

(CTSL 2) Canon TS-E 17mm f/4L UD Aspherical Ultra Wide Tilt-Shift Lens for Canon Digital SLR Cameras

(CTSL 3) Canon TS-E 45mm f/2.8 Tilt Shift Lens for Canon SLR Cameras.

Follow the link Nikon Tilt Shift Lenses for our entire Nikon TS Lenses collection. We recommend several models below:

(NTSL 1) Nikon 45mm f/2.8 Perspective Control-E Nikkor Aspherical Manual Focus Lens – Grey Market

(NTSL 2) Nikon PC-E Micro NIKKOR 85mm f/2.8D Manual Focus Lens – Grey Market

(NTSL 3) Nikon PC-E Micro NIKKOR 85mm f/2.8D manual Focus Lens with 5 Year U.S.A. Warranty, Tiffen 77mm Photo Essentials Filter Kit, Lens Cap Leash, Professional Lens Cleaning Kit.

We suggest also Arsat Tilt Shift Lenses brand of TS lenses for Nikon, Canon, Sony and Minolta cameras.

Fisheye and Fisheye Zoom Lenses

These lenses create special effects even during shooting. Of course, the enthusiast is limited only by imagination for post processing using photo editing software available in our site in Image Lab department.
You see below Canon EF 8-15mm f/4L Fisheye USM Ultra-Wide Zoom Lens for Canon EOS SLR Cameras and two pictures taken with this zoom lens.

We recommend also the popular Canon EF 15mm f/2.8 Fisheye Lens for Canon SLR Cameras with fixed focal length. The schematic below has the picture of the lens and also two sample images made with it.

We recommend Rokinon FE8M-N 8mm F3.5 Fisheye Lens for Nikon, a very popular lens. See below the lens picture and two sample images taken with this lens.

Conclusions

We highlighted some advanced aspects of lenses for digital SLR such as MTF, image stabilization, TS and fisheye. For better understanding of lens features, we explained them in connection to several parameters of image sensors. Our idea is to help the photographers to take a better decision when buying lenses with advanced features and also for using these lenses at their full potential by knowing the basics behind their operation. Obviously, our purpose was not to exhaust the subject, just to reveal several important aspects. We hope that this article will help the photographers and also will stimulate their interest to go in further details.

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Posted in Featured Lenses

Exposure in Digital Photography

Exposure in Digital Photography – Basics

This article reviews several basic aspects of exposure in digital photography for helping beginners and mid-level enthusiasts to get better pictures. More details on this topic are available on Internet and also in very large number of books.

Exposure is the total light energy incident either on film or on image sensor. Physically, this is the luminous flux collected by the lens during the exposure time or shutter speed. You can control the exposure either by changing the luminous flux, or by changing the shutter speed, or by changing both the luminous flux and the shutter speed. You should be aware that from the exposure standpoint there are significant differences between the film photography and digital photography.
In film photography, the exposure changes the film transparency. In digital photography, the exposure creates a voltage across each photo element of the image sensor, proportional to its exposure.
Digital photography should be back compatible with film photography in several aspects. One aspect is film speed, which is a measure of film sensitivity to light, expressed in ISO_number or ISO_speed, such as ISO100, ISO200. Light sensitivity of all digital cameras is also expressed and set in ISO_speed, the same as film sensitivity. The smallest ISO_number has the lowest light sensitivity, but also reveals the finest details in the picture and has the lowest noise level. When increasing ISO_number, light sensitivity increases, but also increases the noise level and the picture has less details.

We explain briefly film sensitivity related to Film Exposure diagram showing the optical density or transparency of the photographic film versus the incident light energy. The optical density graph of the film is nonlinear, as any transmission function. The bottom level of optical density graph is the noise region known as Density of base + fog, inherent in any photographic film and also in any image sensor.

The total amount of light energy incident either on film or on image sensor depends on the light collected by the lens across its entrance pupil expressed by the f/number, and on the shutter speed or exposure time. f/number and shutter speed concepts have their origins in film photography, but they migrated naturally to digital photography with the same meaning. However, exposure sensitivity, f/number and shutter speed are related to light control in photography, including digital photography.
 
Always the lens specs give the minimum f/number as a mean to specify maximum entrance pupil. A lower number such as f/1.2 means a faster lens, collecting twice more light than f/1.4 lens. In the schematic Price Difference Between f/1.2 and f/1.4 Lenses below, the lens with f=50mm, f/1.2 has 41.67mm entrance pupil diameter, but the lens with f=50mm, f/1.4 has 35.71mm entrance pupil diameter. Notice the price difference between these two Canon lenses, only for 0.2 difference in f/number. High price tag of f/1.2 lens comes from special optical elements used for compensating the geometric and chromatic distortions towards the lens boundary.

For the same amount of light coming from the scene, film illumination is controlled by the combination [f/number; shutter_speed] usually known as Exposure Value or EV. In other words, a certain EV can be obtained by any [f/number; shutter_speed] combination which gives the same amount of light energy on film or on image sensor. The schematic Constant Exposure Value – EV below shows several combinations [f/number; shutter_speed] giving the same EV and two pictures shot with this EV. Notice that EV-1 means two times more light than EV, and EV+1 means half the light than EV. The difference in two consecutive EV is known as stop. There is no conflict between stop used as difference between two successive EV values, or between two successive aperture values, or between two successive shutter speed values. Any unit change either in aperture or in shutter speed makes a unit change in EV.

Shooting a picture is always a mix between the camera capability and photographer’s skills, with emphasis on photographer’s side. Light metering is very important on shooting, but the photographer decides either to use EV as suggested by camera, or to do Exposure Compensation – EC. Most of digital SLR cameras such as Canon EOS Rebel T3i 18MP CMOS APS-C Sensor DIGIC 4 Image Processor and Nikon D7000 16.2MP DX-Format CMOS Digital SLR to name just two very popular models have EC feature. EC is done totally according to photographer feeling for altering the camera decision on f/number and shutter speed based on factory provided algorithms. Several hints about EC are provided later in this article. When EC increases with one stop, EV decreases with one stop, allowing more light to illuminate the image sensor. All digital SLR cameras have EC features. The popular models Canon EOS Rebel T3i 18MP CMOS APS-C Sensor and Nikon D7000 16.2MP DX-Format allow EC span from -5EV to +5EV in 1/3 EV or 1/2 EV steps.

The lens aperture is the circular opening into lens diaphragm located in lens optical center which controls the exposure by controlling the luminous flux. Having an adjustable size like human eye iris, lens diaphragm is sometimes called iris diaphragm, or simply iris. The f/number usually known as stop, is part of a sequence such as f/1.2, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32 where denominator values approximate powers of square root of two. Each stop corresponds to an aperture size. When changing from one stop such as f/2.8 upwards to f/4, the aperture area halves, which reduces to half the luminous flux through the lens. The math is simple: if the aperture follows the rule of powers of two, its diameter follows the rule of square root of two. When the stop changes from f/2.8 downwards to f/2, the aperture area doubles and two times more light goes through the lens.
Besides controlling the light flux through the lens, the aperture is also an optical element of the lens, controlling its depth of field – DOF. In the schematic Constant Exposure Value – EV, both pictures aim the same subject, illumination conditions and EV are identical.
The left-hand side picture was shot with slow shutter such as 1/15 and with small aperture such as f/16. The scene has large DOF, with details in the background and with water drops looking like a bunch of thin strings. You should be careful with too small-size apertures beyond f/8. The picture might loose sharpness or details versus a picture shot with high aperture such as f/1.8, because of diffraction.
The right-hand side picture was shot with high speed shutter such as 1/1000, but with large aperture such as f/2. You see a shallow DOF with well focused “frozen” water drops in the front, but with a blurred background.

The light going through the lens reaches the image sensor during the time frame of opened shutter, or shutter speed. Typical numbers for shutter speed in seconds, are: 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000. For high-end digital SLR cameras such as Canon EOS Rebel T3i 18 MP and Nikon D5100 16.2MP CMOS Digital SLR, shutter speed sequence spans from 30s to 1/4000.

The schematic Shutter Speed and f/number Examples has pictures of the same scene, with the same illumination, but shot with different exposure conditions, each picture having its EV. Across each row, f/number is constant, but the shutter speed goes from fast to slow as specified in schematic. Obviously, within the same row, the pictures are lighter toward slower shutter. Across each column, the shutter speed is constant, but f/number increases upwards. Accordingly, the pictures are going from lighter on the bottom side to darker toward the top side. In conclusion, we notice two extreme situations: underexposure on top left side of the schematic and overexposure on bottom right side. In-between these extreme cases, there are more or less acceptable exposures of the scene.

The regions of underexposure and overexposure of photographic film are marked with their respective names on Film Exposure graph.

The schematic Image Sensor Response to Illumination shows the structure of Foveon X3 CMOS color image sensor and the graph of voltage generated across a single image sensor versus the luminous flux incident on it, expressed in number of photons. The image sensor has several major differences versus the photographic paper:

(IS1) The image sensor consists of large number of discrete individual sensors or pixels. Across its surface, each pixel samples part of the image incident on it.

(IS2) The incident luminous flux on each sensor generates a voltage proportional with the illuminance, following almost linear dependence.

The human vision is able to see from very low light level such as starlight when there is no color perception, up to bright sunlight. This is a very high dynamic range of 10,000,000,000 in power, or over 100dB in ratio, or about 33.2 stops.
Some high-end negative films such as Kodak Vision3 have a dynamic range of 11,500 or 13 stops.
The dynamic range of LCD displays widely used as rear digital camera displays, computer monitors and TV sets, commercially referred to as contrast ratio is about 1000:1, or 9.5 stops.

We recommend several advanced digital cameras such as Canon EOS Rebel T3i 18MP CMOS Digital SLR Camera and Nikon D5100 16.2MP CMOS Digital SLR Camera span light sensitivity across 14-bit range, or 16,384:1, or 14 stops. However, tonal gradation of 14 stops is satisfactory for vast majority of situations.

The schematic Image Sensor Response to Illumination shows also the dynamic range of human eye of 33.2 stops, which is larger than the dynamic range of photographic paper, of the image sensor and also much larger than the dynamic range of LCD displays. The purpose of photography is to catch on picture the reality as faithful as possible. The biggest problem in photography is to compress or squeeze the dynamic range of eye perception in the dynamic range of the image sensor and also in the dynamic range of picture displayed on LCD screen and printed. This problem appeared first in film photography where the compressing technique is known as tone mapping. The Film Exposure schematic shows the optical density zones used for matching the picture on photographic paper with the real world seen by human eye. The interested reader can follow the links to find more about tone mapping and zones system.


The pictures above span the entire tonal range of respective cameras as marked on each schematic. However, tonal range of the real life is larger than shown by pictures: we cannot see details in bright areas and also in very dark areas. The schematic below shows two examples of digital pictures containing dark areas and also bright areas. Most digital cameras today show at request the picture histogram. The histogram shows on horizontal axis tone levels or simply tones and on vertical axis shows the number of pixels for each tone value. Maximum number of tones depends on camera model. Digital cameras such as Canon EOS digital SLR series and Nikon D5100 16.2MP CMOS Digital SLR Camera use 14-bit or 16,384 levels analog to digital conversion of signals from image sensor. Accordingly, the maximum tonal value on histogram follows the analog to digital conversion accuracy of the camera. The bottom picture was underexposed on purpose. In its histogram you see more pixels in dark areas and practically no pixels in bright areas.

Some high-end digital SLR cameras such as Nikon D5000 12.3MP DX Digital SLR Camera
provide at request either tonal histogram as in schematic below:

or color histograms across a select area of the image, as in schematic below:

What is a histogram good for? Usually, people ignore the image histogram, unless there are situations when should make a decision on exposure, and how to change it. The schematic Exposure Cases below has three pictures and their histograms, in three situations: normal exposure, when the histogram maximum is roughly at mid tonal range, underexposure when the histogram maximum is shifted toward dark zone, and overexposure when the histogram maximum shifts toward light zone.

The picture expected by photographer depends on light metering and on the exposure modes.

Normal exposure is computed by digital camera based on light metering selection of the photographer. The real life scenes could be very different from one shot to another. The illuminance can be from very faint up to very bright across the entire image projected on image sensor, spanning more than the entire tonal range supported by the image sensor. Finding the optimum exposure across the entire image is a real challenge even for most sophisticated systems. The schematic Light Metering Zones shows light measuring points grouped in areas of light measuring interest and symbols of their use when selecting light metering modes. As we mentioned before, the right exposure is always a combination between the photographer’s skills and the camera capability. According to the scene content and to the subject, the photographer selects one of light metering options as shown in Light Metering Selection schematic.


In Evaluative Metering mode, the camera measures the light with a large number of dots located within a grid across the entire image. In some high-end digital SLR cameras such as Canon EOS-1D X 18.1MP Full Frame CMOS Digital SLR, the matrix measuring sensor can have up to 252 distinct elements for general metering, with 35 elements used for low-light metering. With illumination information collected from all the elements spread across the image and based also on ISO_speed, the camera computes f/number and shutter speed according to the exposure mode selected by photographer. Evaluative metering is recommended for most shooting situations.
In Partial Metering mode, the camera measures the light within the circular region around the center. This mode is recommended for scenes containing bright and also dark areas. Based on the light measurement across aimed area and on selected ISO_speed, the camera sets the f/number and shutter speed.
Center-Weighted Metering mode is recommended for subjects positioned in center of the image.
In Spot Metering mode, the camera measures the light with a specific sensor selected by the photographer from the entire sensor matrix. The selected sensor is highlighted by camera in the spot metering pattern visible in the view finder. For better visibility in Light Metering Selections schematic, the sensor is surrounded by a red circle. In this case, the photographer is particularly interested in the exposure within the area centered on the selected light measuring point.

After selection of light metering modes, the photographer selects one of the exposure modes common to most of digital cameras, such as:
Auto and Scene modes, when the camera selects automatically the ISO_speed, f/number, shutter speed and focus on the closest part of the scene.
P – Programmed Auto, when the camera adjusts automatically f/number and shutter speed for optimal exposure. The photographer has the freedom of manual selection of the combination f/number and shutter speed which keeps the same EV.
S or Tv – shutter mode, when the photographer selects the shutter speed and the camera finds the f/number for optimum exposure.
A – aperture mode, when the photographer selects the f/number and the camera finds the shutter speed for optimum exposure.
M – manual mode, when the photographer selects both the f/number and the shutter speed according to personal preferences.

Normal Exposure uses factory defined algorithms for selecting f/number and shutter speed. In many situations, normal exposure gives correct exposures. There are still situations when normal exposure is not the right answer for f/number and shutter speed combination. The large diversity of scenes and of subjects within the scenes require also photographer’s correction of Normal Exposure outcome.

In white dominated scenes, Normal Exposure goes toward darkening the picture, as seen in Exposure Compensation Examples schematic. The photographer must add some EC steps to shoot a good picture. There are available either 0.3EV or 0.5EV steps for EC. Referring to Image Sensor Response to Illumination schematic, with Exposure Compensation the photographer shifts EV span upwards, starting from above the DARK level and going beyond the BRIGHT level. Now the details hidden initially below DARK level become visible, but of course the details above BRIGHT level become invisible. The photographer can see EC outcome either looking at the picture on rear camera LCD, or looking at the pictures histograms before and after EC. If not satisfied, another EC is required. The picture is brighter when increasing EC and darker when decreasing EC.
In dark dominated scenes, Normal Exposure goes toward lightening the picture. The photographer must subtract some EC steps for having a nice picture, as seen in Exposure Compensation Examples schematic. Referring to Image Sensor Response to Illumination schematic, using EC the photographer shifts downwards EV span, starting from below the BRIGHT level and going beyond the DARK level. After EC, the details hidden above BRIGHT level become visible, but of course the details below DARK level become invisible.

WARNING: Picture quality must be improved before shooting, for revealing the details in the picture within extreme exposure areas, either dark or bright. There is no image editor able to reveal details from a badly exposed picture. That picture does not contain the expected details!

The EC situations of images explained above should work fine until the subject losses its patience! Exposure Bracketing is required for shooting a scene with areas illuminated beyond the tonal range of the image sensor. Referring to Image Sensor Response to Illumination schematic, the Normal Exposure with EC=0 covers a window of only 14 stops, which is the tonal span of the image sensor. For catching tones beyond full tonal span of Normal Exposure upwards and also downwards, you must shoot the same scene with different EV, usually with one or two stops higher and lower. In this way, you get the pictures with Normal Exposure and also underexposed and overexposed pictures of the same scene, as you can see in Exposure Bracketing schematic. Using one of the image editors available in the Photo Editing Software section of our Image Lab department, you can build stunning High Dynamic Range – HDR pictures.

Exposure in digital photography is very extensive subject. This article highlighted only the main aspects such as light sensitivity, light metering and exposure compensation. There are also other aspects, such as selection of aperture, shutter speed, HDR photography, to name just a few which will be covered in future articles. We invite the readers to express their opinions about this article and also to suggest us other subjects for future articles.

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Posted in Exposure - Digital photo

Lighting – Color

Lighting in Digital Photography
Colors of Light Source and of Pictures

This article highlights some basic aspects related to color in digital photography for improving the knowledge of photography fans. We put together into an organized form several aspects very well known in digital color photography with links to relevant Internet sites when clarification requires more space. There are probably at least several thousands articles related to this subject on Internet and not only. We hope that this article will rise interest for further reading on Internet and elsewhere and will also nurture some useful discussions.

The Digital Picture Flow Chart schematic summarizes this article. Digital picture is a two-step process as it is any classical picture: shoot the picture and see the picture.

Step 1. Shoot the picture

We consider a simple case of an operator shooting a scene illuminated by sunlight at noon. The scene reflects the sunlight toward the operator’s eyes and also toward his/her digital camera, situation labelled A in Digital Picture Flow Chart schematic.

The operator sees the color scene with his/her eyes and his/her brain. This combination is by far better than any existing digital camera, because is based on human experience and thinking.

The digital camera uses a lens that makes the image of the scene on its color image sensor. We correctly assume only geometric distortion introduced by the lens and no color distortion. The color perception of the image sensor is based on additive RGB color model, with Red, Green and Blue as primary colors. According to this model, the white light from any source can be synthesized from the primary colors, as shown in Additive Primary Colors diagram.

The schematic sRGB Color Triangle shows the loci of primary RGB colors or wavelengths and their relative intensities as defined by the additive color model. The point D65 is considered pure white as the outcome of summing theoretical primary colors according to a relationship between their intensities defined by the additive color model. In reality, theoretical primary colors are very difficult or impossible to get at the wavelengths defined by the additive RGB model and at reasonable price for large dissemination of color light emitting devices. Instead, there are used other three available RGB colors close to primary colors. By consequence, with available colors the addition outcome is not pure white. However, there is a quite narrow region around D65 point where white is acceptable with faint tones, usually either toward yellow or blue. Accordingly, all colors across the entire picture are changed. The generic color sensor of digital camera is shown in the schematic below.

The color sensor has a mosaic-type color filter layer on top of photo sensitive elements or pixels for making three monochrome replicas in Red, Green and Blue of color image incident on image sensor surface. Each monochrome replica has smaller number of pixels than the incident color image, but the total number of pixels of all three Red, Green and Blue images is equal with the number pixels of the color image. In other words, the mosaic color filter re-samples the incident color image in separate Red, Green and Blue images with lower spatial resolutions. It is very important to mention several aspects of mosaic color filter:

(i) The mosaic filter has Bayer filter configuration based on additive color model, which also mimics the light perception of human eye. In Bayer mosaic filter, from the entire image sensor area Green elements cover 50%, Red and Blue elements cover 25% each. This article will consider only Bayer mosaic filter. There are in use now several variations of Bayer filter with different colors and their arrangements, but considering them, too, is far beyond the scope of this article. Those interested in this subject can look further on Internet or somewhere else for more information.

(ii) Each element of mosaic filter overlaps perfectly only one pixel. It is obvious that the color information is encoded across the entire area of the image sensor.

(iii) We assume for now the digital camera white balance selection in SUN position. When the operator presses the shutter button, the image sensor makes inside it an electronic image, which is the replica of the optical image on its surface made by the lens and filtered by the mosaic filter. Obviously, the electronic image appears during the exposure time. Setting the duration of exposure time will be the subject of another article.

(iv) The digital image controller reads the electronic image from sensor and decodes the information from pixels using demosaicing algorithms for obtaining the entire color picture in RAW format which contains maximum information about the picture. This format is not yet readable by any display device or printer. RAW format is the electronic equivalent of negative in film photography. Using their proprietary software, most manufacturers of digital SLR cameras make available RAW format to users for further processing on computer. Usually, professional photographers and high end amateurs use RAW format and additional software applications to process images starting from RAW format and saving their work in widely accepted .jpg, .jpeg, or .jpe compressed format. All digital cameras process further the RAW format for delivering pictures in very familiar .jpg, .jpeg, or .jpe format.
We kept this description of converting the optical color image in electronic file as short as possible, to not harass the reader with too many details. For those interested on this subject, we recommend further reading on Internet or somewhere else. However, even from this simple and short explanation, you realize the multitude of sources of errors only during the process starting with the optical image of the scene incident on image sensor and ending with the “trivial” .jpg file.

(v) Further, .jpg file is used by vast majority of display devices such as LCD rear camera monitors, LCD computer monitors, by printers and in certain conditions by LCD TVs, plasma TVs and digital projectors.

digihut.org recommends Canon EOS Rebel T3i Digital SLR Camera with 18MP CMOS APS-C Sensor, DIGIC 4 Image Processor, 3.0-Inch Vari-Angle LCD (Body Only) and Canon EF-S 55-250mm f/4.0-5.6 IS II Telephoto Zoom Lens for Canon Digital SLR Cameras. Below are pictures of recommended products and sample pictures made with this camera and lens combination.


Step 2. See the picture

Obviously, the operator takes a look at the scene before shooting it and remembers the scene. After shooting the picture, the operator looks at the picture of the scene displayed on several devices labelled in Digital Picture Flow Chart schematic such as:
(i) rear camera LCD, labelled B
(ii) LCD computer monitor or TV, labelled C
(iii) on-screen projection from digital projector, labelled D
(iv) printed scene on photographic paper, labelled E.

Both display devices B and C use LCD technology which will be reviewed briefly using the schematics below. A careful look at any LCD screen reveals vertical color stripes such as in Color LCD Pixels Pattern schematic. The encircled area is a color pixel. When zooming it as in Zoom LCD Color Pixels schematic, we see the R,G,B sub-pixels structure used to generate the multitude of colors of the color pixel according to additive color model. The color pixels are used to build the entire pattern of color stripes of LCD screen.

The schematics above shows color LCD from the front side or viewer side. The LCD is illuminated from the backside with light emitted by a white source such as LED, Electroluminescent panel (ELP), Cold Cathode Fluorescent Lamps (CCFLs), Hot Cathode Fluorescent Lamps (HCFLs), External Electrode Fluorescent Lamps (EEFLs). LED-based backlights color LCDs come in two options: either several white LED illuminating the entire screen, or each sub-pixel is a single color LED.
IPS technology uses transistors for individual addressing of transparent sub-pixels working as light valves. Both the transistors and the filters are built on a thin film transparent layer attached to the screen. Each sub-pixel is also a band pass filter for respective Red, Green and Blue primary colors according to RGB additive model. Practically, each of these colors are slightly off the required wavelengths, therefore the resulting white is not pure. It is obvious that the white of the highlighted color pixel in Zoom LCD Color Pixels schematic depends on the colors of back illumination source and also of the colors of Red, Green, and Blue sub-pixels. This color is located somewhere as close as possible to D65 point. There is a tremendous effort of display manufacturers for generating the white color as close as possible to D65 point, thus achieving the best color purity.
In summary, assuming that the LCD color monitor has a perfect color signal at its input, the displayed image depends strongly on the LCD monitor or LCD TV.

digihut.org recommends ViewSonic VX2250WM-LED 22-Inch Widescreen Full HD 1080p LED Monitor with Integrated Stereo Speakers and VIZIO E3D420VX 42 Inch Class Theater 3D LCD HDTV with VIZIO Internet Applications shown below.


Sometimes you can display on Plasma TV your video clips and movie productions. On the Digital Picture Flow Chart schematics, plasma TV known also as Plasma Display Panel TV or PDP TV is on the same C category as light emitters, such as LCD TV.

PDP TV has the same color pixel and sub-pixel structures as shown in Color LCD Pixels Pattern and in Zoom LCD Color Pixels schematics. The major difference is in generation of R,G,B primary colors. Plasma Display Panel Schematic shows the basic elements for generating each R,G,B sub-pixel. The entire PDP consists of an enclosure filled with neon at low pressure and a matrix of address electrodes and display electrodes shown in schematic as yellow stripes. The R,G,B color sub-pixels containing the respective color R,G,B phosphors are located at the overlapping areas of address and display electrodes. A single specific color pixel is activated by addressing simultaneously one display electrode and all three R, G and B address electrodes behind the sub-pixels of that specific color pixel. A glow gas discharge appears between the display electrode and each of R, G and B address electrodes and accordingly, the Red, Green and Blue phosphors are emitting light with intensity dependent on the voltage between the overlapping electrodes. You noticed that pixels of PDP are light emitters, not band pass filters as in most LCD panels. It is easy to notice that color matching issue between R,G,B colors of PDP and primary colors of additive RGB color model still remains.

digihut.org recommends Panasonic VIERA TC-P65GT50 65-Inch 1080p 600 Hz Full HD 3D Plasma TV shown below.

At this point, some comments on pixel size of digital cameras and displays are welcome.
As you notice in Color Image Sensor Schematic, the image sensor is an array of individual sensors or pixels which take as many samples from the continuous image on it, as many pixels are. Rendering image details in digital photography and video is related to center-to-center pixel spacing. Smaller pixels spacing gives more details of picture made by digital camera or by video camera. In other words, if two image sensors have the same size, the sensor with more pixels gives an image with more details. Commercially, digital cameras are advertised by the pixel count of the image sensor, often not mentioning the sensor size. A digital SLR camera with 18MP and a digital point-and-shoot camera with 16MP have good rating at the time of writing this article. For the same reason, the pixel count is used also to advertise camcorders. A good camcorder has a pixel count of 8.9MP or higher.

The situation is different with computer monitors and digital TV sets. Actual models of computer monitors and HDTV sets should be compatible with both 4:3 and 16:9 aspect ratios. HDTV sets have three options: 1080p, 1080i or 720p. Regardless of screen size, the number of pixels is the same in each category. Therefore, the pixel size depends on screen size. However, HDTV has maximum 2MP on its screen. A medium-size, good quality picture from a digital camera has 3456×2304 pixels, which must fit in maximum 1920×1080 pixels. When you see the image on computer monitor, the computer does picture interpolation to fit the screen. When you connect the digital camera directly to TV, the camera does the interpolation. Of course, during interpolations fine details of the image are lost and the colors are degraded, too.

Retina Display of Apple iPads have higher pixel count than required by HDTV requirements, for pleasant appearance. By consequence, Retina Display does not appear pixelated if you look at it from a normal distance. However, even Retina Display does not have enough pixels to match the number of pixels of medium-size good quality digital picture, and the interpolation is required. All the other color-related aspects discussed above apply also to Retina Display.

digihut.org recommends Apple iPad MC705LL/A (16GB, Wi-Fi, Black) shown below.

As partial conclusion, the operator which shot the picture and still remembers it, sees the color differences between the object and its picture displayed either on rear camera LCD, on LCD computer monitor or on HDTV.

Digital projector is another option to see the digital pictures, labelled D in Digital Picture Flow Chart. These devices are also emitters producing the colors according to additive RGB color model. We will summarize here some basic aspects related to colors related to digital projectors. For more information on operation of digital projectors, the reader is invited to follow the link. Commercial digital projectors use three technologies.
a. DLP or digital light processing technology is based on a multitude of mirrors for reflecting the light coming from color LED in most situations. DLPs are used typically for conference room presentations, but they can be used home, too.
b. LCD projector technology uses one LCD light valve matrix for each R,G and B color. Red, respectively Green and Blue LEDs are used as light sources. The color projection on screen follows also the additive RGB color model. Obviously, the color problems are similar with LCD TVs. However, LCD video projectors are used for home and business.
c. Liquid crystal on silicon (LCoS or LCOS) technology uses reflective LCD light valves, a single white light source and RGB filters for primary colors. Commercially available LCoS video projectors have portability advantage.

digihut.org recommends you ViewSonic PJD5133 SVGA DLP Projector – HDMI, 2700 Lumens, 3000:1 DCR, 120Hz/3D Ready, Speaker, shown below.

All color display devices such as computer monitors, TVs and digital projectors require calibration before use, and eventually periodic adjustments.

We suggest you a simple exercise: Look at the image on laptop screen and also on an external LCD monitor connected to it. You notice the difference, which is normal, even after doing color calibration on each monitor. Based on their previous experience and also on the lack of knowledge of real scene, people ignore small changes of colors and do not pay too much attention to color in white areas. They just take the picture as it is, if the relationships between colors make sense according to their previous experience. Only non-sense colors raise concerns. The human brain operates in this way.

We consider now the situation E of the Digital Picture Flow Chart, when the operator sees the printed picture. This is the particular case of looking at any object which reflects the light. The CMYK color model is used for modeling the human color perception of any light-reflective object. CYMK is a subtractive color model based on the selective reflection of colors by an object illuminated with broad band light, not necessarily with white light. In other words, the object subtracts the reflected colors from the incident light. All other colors of the incident light are absorbed by the object.

CMYK subtractive color model uses Cyan, Magenta, Yellow and Key (black) as primary colors for creating the entire subset of colors or gamut at printing. In the Subtractive Color Mixing schematic you see in the lobes the color outcome of combining primary colors. By combining all three CMY colors such as in the center of the diagram, the outcome is gray, which is non-saturated black. Black is used additionally in printing for enhancing grey tones up to black level. There are two main aspects related to printing: color and sharpness. We comment color first.

Inkjet and laser are dominant color printing technologies on the market.

Inkjet printing, as the name suggests, throws on paper under very strict control, extremely fine droplets of Cyan, Yellow, Magenta and Black ink for printing text and pictures. Digihut.org has more than 1,500 inkjet printers to choose from. Some inkjet printer models such as Epson Artisan use six colors instead of four for delivering more brilliant colors.

Laser printing process is based on the xerographic printing process. This process consists of creating the electrostatic image of the document or picture to be printed on the surface of a rotating drum. A sharply focused laser beam is used to make this image. Extremely fine particles of toner are stuck on the electrostatic image on drum surface, which are further transferred to paper and fixed on it by heating. Digihut.org has more than 5,000 laser printers. Toner thickness on paper gives color saturation.

Natural appearance of picture colors or gray tones and details rendering are the other important feature of printing. Paper smears ink more than it smears toner. In other words, a dot in the image becomes a spot during printing, which can degrade significantly the details of printed document. Printer quality expressed in dots-per-inch or dpi is standard parameter for rating printing details and also for advertising printers for pleasant appearance of printed document. Photo quality printers have 4800dpi or more.

Photo quality paper has special coating on one side with practically no smearing. Photo paper with various finish such as luster, glossy, semi-glossy, matte, give rich colors with the same look and feel as traditional photograph. Ink-jet photo printers are more popular than laser photo printers, based on price-performance trade-off. Accordingly, inkjet printer paper is used more than laser printer paper.

All color printers require calibration before use, and eventually periodic alignment checkup.

digihut.org recommends Canon Pixma iX6520 Inkjet Printer, shown below.

Light Sources

At the beginning of this article we supposed the scene illuminated with sunlight at noon, and we kept this supposition throughout the entire article. Sunlight at noon is considered white light. Multiple situations are encountered in real life, when the scene is illuminated with various light sources. We will review briefly the most relevant cases. The digital SLR cameras have White Balance selection, for informing the digital image controller of the camera about the light source at the time of shooting. The camera controller makes automatic color adjustments according to standard spectrum of the selected light source from an option list such as:
(s1) auto balance
(s2) daylight
(s3) shade
(s4) cloudy
(s5) tungsten lamp
(s6) fluorescent
(s7) flash, either built-in, or recommended by camera manufacturer
(s8) custom (use this for best results if not shooting in sunlight)
(s9) color temperature (for advanced users only)

If White Balance is properly set, your pictures will have amazing colors. The digital cameras are doing this job very well.

WARNING The light sources listed above are given as examples. Check to see what are the selections of your camera.
Always check the White Balance setting before shooting. A badly shot scene cannot be corrected.

Sunlight early in the morning or toward sunset has more red. Accordingly, if the photographer does not take special precaution, the picture will change the entire gamut toward red. Usually, digital SLRs have options to adjust light source color within certain rage departing from factory-defined options shown above. However, the best is custom correction, shooting conditions permitting. Follow the instruction manual of your digital camera. For insufficient light, use speedlite flash either built-in, or as stand alone unit. For stand alone unit, use only the speedlites suggested to work with your camera. Stand alone speedlite make dialogue with the digital camera for delivering only the required light flux for the best exposure. If the digital camera is not able to make the dialogue with the speedlite, most chances are for strong overexposure.

digihut.org recommends you Canon Speedlite 430EX II Flash for Canon Digital SLR Cameras and Nikon SB-600 Speedlight Flash for Nikon Digital SLR Cameras shown below.

Conclusion: in real life, the colors of the same elements of the scene are not the same in all display devices! We are always making the best effort to see the pictures on computer monitor, HDTV, digital projector and on photo paper as natural as we can do. However, based on their previous experience, the humans do not notice the small departure of colors from the real ones. The quality of entire picture is evaluated according to its overall appearance.

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Posted in Lighting

Lighting – Position

Lighting in Digital Photography
Positions of Light Source, Object and Camera

A good photo doesn’t need any change. A bad photo will never be good.

This article deals with very basic aspects of positions in digital photography only. It targets the amateurs and does not claim at all to exhaust the subject even at this level. Just it brings to the reader’s attention some basic aspects for making good pictures when shooting with digital camera. We hope this article will raise interest for comments within this site and for further reading on Internet and elsewhere.

Simply put, assuming that the object is not a light source such as lamp, there are three main elements in photography: light source, object and camera.

The light can come from different sources such as: (i)direct sun, (ii)cloudy sun, (iii)sunlight reflected by large objects or surfaces; (iv)incandescent bulb; (v)fluorescent lamp; (vi)lamps used to illuminate the streets, (vii)LED or (viii)speedlite or flash. Throughout this article we prefer to use speedlite instead of flash, to avoid confusion with flash memory. This enumeration of light sources is based on the color of each category. It will be a separate article about the color of light sources and its impact on colors of digital pictures.

There are two major aspects related to light in digital photography:
positions of the light source, of the object and of the camera, and
color of the light source.
This article covers only the positions aspect, summarized in Position schematics, with examples of portrait pictures.

Take note that this discussion about positions holds true for any color of the light source.

It is important to mention that the light source in all Position examples has small size, such as a bulb. For outdoor shooting, even the Sun is considered a small size white light source with parallel rays. If you look at the Sun through a strong absorption filter, it appears quite small comparing with a person or with a landscape size.
In all Position pictures, the transitions between light and shadow are sharp, which should be avoided for obtaining a pleasant portrait, unless the photographer takes advantage of shadows for highlighting some object features. Just compare any picture in Position examples with the picture in Diffused Sunlight example, where the picture was taken outdoor, in slightly cloudy sky.

Everybody wants to shoot nice pictures. This is not very difficult to do if the photographer pays attention to some common-sense aspects. In sunlight, the pictures are vivid with natural colors. For a good picture, the photographer must look carefully for smooth transitions from light to shadow on the object. In Diffused Sunlight example, the light from the Sun was scattered by clouds, which became an extended or broad light source, producing smooth shadows on the object. In the Diffused Sunlight example, you can easily depict the position of the Sun, but the picture is pleasant.

For indoor portraits, the shadow can be controlled better by using extended light sources such as softbox and studio light source as extended light sources. Below you see examples of both soft sources. The softbox make soft transitions between light and shadow on the object. The studio light source makes a light spot with soft boundaries on the object for highlighting a particular area.

Be aware of using studio lights: a softbox gives a single smooth shadow per object feature as you can see on the Smooth Shadows examples below; replacing the softbox with multiple studio lights might make multiple smooth shadows of the same feature of the object.

The picture at the left hand side was made using multiple softboxes and also several diffuse reflection panels. For the picture at the right hand side, the photographer used several sources with different colors making diffuse illumination at different angles, as it can be depicted easily.

The softbox can be used also for mitigating the shadows in outdoor shooting, as you can see below. The benefit is obvious.

Several light sources and accessories for diffused light illumination are shown below.

Here is an example of photo studio using softboxes.

By using the speedlite, either with a flash diffuser or with a speedlite softbox you get astonishing soft shadows and a natural integration of the object into its background.

Back light illumination is often encountered when shooting either indoor, or outdoor. When the object is back illuminated, the object side facing the photo camera is strongly shadowed by the object itself. Vast majority of digital cameras have an embedded speedlite. The embedded speedlite will illuminate the object side facing the camera, but will eventually introduce also shadows on the object, because its light is not scattered enough. It is a widespread perception, that the speedlite is used only when there is not enough light for reasonable shooting, either indoor or outdoor, usually indicated by camera. This is partially true. Some comments will clarify the issue.
If the photographer wants to do a quick shot for a reasonable quality picture, it is OK to use the speedlite in this way. The picture will have some shadows with sharp transitions, expected and accepted by the photographer. If the subject is a person or an animal looking straight at the camera during shooting, the eyes could have red spots or red eyes removable further by a multitude of means. Many cameras have the option for red eyes reduction. We suggest the use of the built-in speedlite as it is for object illumination only when you do not have a better choice.

More interesting is the situation when the photographer wants to shoot a good picture either indoor, or outdoor, using a standalone speedlite. This option is always better. All embedded speedlites illuminate the object straight, eventually producing shadows with sharp edges. Practically, there is no way of attaching any light diffuser to the embedded speedlite. The situation is totally different for the standalone speedlites, having available specially built accessories such as diffuser and softbox, as you can see in Speedlite, Softbox and Diffuser picture above. The speedlite diffuser gives very good diffused light, is easy to handle and to carry on top of the speedlite. For indoor shooting, it is better to direct the speedlite head toward the ceiling, for taking advantage of further light scattering by the ceiling. Do not worry abut underexposure. Good speedlites are strong enough and they have a dialogue with the camera through the hot shoe. The speedlite measures the back reflected light from the object, and the camera stops the speedlite lamp when the proper illumination was reached. Having attached either a diffuser or a softbox, the speedlite can be aimed to the object; no worries about shadows.
Just look at the example below to see the difference between the back light illuminated pictures shot without speedlite or flash and with speedlite.

Landscapes are illuminated either by sunlight, moonlight and sometimes by streetlights. These three main lighting categories are very different; therefore there will be different comments for each of them.
For landscapes shot in daylight, side lighting is preferable. In the example below, the shadows highlight some elements and give three dimensional aspect of the picture.
Top lighting might emphasize a certain area of the picture. In this way, the photographer could send a message to the viewer.
Front lighting gives a strong perception about depth; the shadows are very long. For this type of shooting, be aware that the direct sunlight may compromise the entire picture. The use of a graduated neutral density filter is a must.
Back lighting can produce astonishing pictures, too, when balancing properly the strong illuminated areas with some shadows.

Moonlight is very dim; therefore, the exposure times are long in nighttime shooting. Quality moonlight shooting requires a tripod, even when using high ISO speed such as ISO6400 and up. Low speed ISO100 or lower are suggested for revealing picture details and low noise, thus requiring tripod. Image sensor area should be as large as possible to collect as much light as possible, such as in digital SLR cameras Canon EOS Rebel T3i, Nikon D5100 and similar, or in full frame digital SLR cameras, such as Canon EOS 5D Mark III, Nikon D800 and similar. The lens should have small f/#, and the diaphragm should be as wide as possible. Lens focused at infinity gives the best results, with a large depth of field. If the picture include the Moon, pay attention to its move in the sky. Longer exposure times might elongate the moon, something you do not want to happen!
Be aware also of the noise (grains) in the image: higher ISO speed means more noise, but ISO100 or lower gives the best results. Shutter release is also very important: triggering the shutter should not move at all the camera.
Shooting streets in the night requires attention to the light from closer lamps, which may affect the shutter speed. As a rule of thumb for any nighttime shooting, take several shots of the same scene with different shutter speeds and focusing. Do not rely totally on the camera auto focus in this case; try manual focus, too. Later you will select the best picture.
You have below several examples of beautiful night pictures.

Obtaining good pictures in different illumination conditions is definitely related to photographer skills, which requires passion and experience.

Hopefully, this article is useful and triggers the attention on some light related aspects in digital photography.

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Digital Cameras

Digital Camera Basics

Rev. 1
 

People enjoy more and more digital photography and video. The use of digital camera and camcorder gives even more satisfaction when the user gets better pictures and videos. We believe that the best way to improve users’ skill is through better understanding of how digital camera works. The purpose of this article is to reveal some basic aspects of digital cameras and give some suggestions for using them better.

There are plenty of references about the digital cameras with pictures, schematics and graphs. Anybody can go to Internet and make a search on digital cameras using various search engines. The outcome will be several hundred thousands if not millions of results covering a multitude of direct and related aspects.

This article summarizes the main functional elements found in digital point & shoot cameras and in digital single lens reflex – SLR cameras. We do not claim complete coverage of the subject; we only highlight the main aspects of digital cameras. We like to think that this article can trigger further investigations for those interested to find more information. The reader is strongly encouraged to post comments on this article and also to tell us what particular topics we should comment in our future articles. Thank you in advance for your help.

Digital P&S camera is the modern version of popular viewfinder cameras for films. In digital P&S camera, the lens makes the image of the scene on the image sensor built either in CCD technology, or in CMOS technology. Some recent digital P&S camera models such as Canon PowerShot A1300 16.0MP Digital Camera with 5x Digital Image Stabilized Zoom 28mm Wide-Angle Lens and 720p HD Video Recording, still have an optical view finder matching the viewing angle of the lens, like its film ancestors. Optical viewfinder gives you the freedom of good framing the scene even in the sunlight. Obviously, you have also available rear LCD for viewing the scene, as most of digital P&S cameras have. Definitely, we recommend this camera to our readers.

Digital Cameras Schematic shows on the right hand side the main elements of typical digital PS cameras. Vast majority of the digital PS cameras, such as Canon PowerShot S100 12.1MP Digital Camera with 5x Wide-Angle Optical Image Stabilized Zoom use only rear LCD for displaying the scene aimed by the lens, at the expense of battery drain. We recommend also this camera, which is pocket-friendly and has the most advanced DIGIC 5 Image Processor. Keep in mind that there are always problems watching the picture on LCD in bright ambient light.

Do not forget: LCDs draw significant amount of power from the battery in any digital camera. For preserving battery life, it is better to turn ON the back LCD only when you need it.

Briefly, for most situations, AUTO shooting mode gives reasonable quality pictures. This article suggests you several aspects for better use of your digital PS to get consistently good quality pictures with a little effort.

All digital PS cameras have lenses with optical zoom and there is also electronic zoom. For good quality picture, we strongly suggest to use mostly the optical zoom. When enlarging the image beyond the boundary of the optical zoom, the camera goes automatically into the electronic zoom mode, which may blur the image significantly if enlarging too much. Higher electronic zoom gives more blur. When shopping for your digital PS, look at the minimum focal length and also at the zoom factor of the lens. Lenses with short focal length have wide viewing angle and vice-versa. Be aware that short focal length may distort the image toward its sides. Optical zoom inherently decreases the picture sharpness toward longer focal length, but the picture has less distortions toward the sides. There are no ways to change this: it is a matter of physics. Only lenses for digital SLR cameras reduce these distortions.

When shooting, press gently the shutter button half way first and wait one or two seconds to allow the lens for focusing the image and eventually for allowing the camera to set properly the ISO_speed, the exposure f/number and shutter speed. You feel half-way position of the shutter as a slight resistance of shutter button at your finger. When you shoot static scenes, several half-way trials give even better exposure parameters such as ISO_speed, f/number and exposure. Keep in mind that image focusing requires mechanical movement of some elements of the lens; therefore, it requires some time to settle. Do not push the shutter button too fast; you might get blurred pictures. Eventually, the camera “tells” you “when” to press further the shutter button.

For shutter speed slower than 1/60, we recommend using a stable tripod for obtaining good quality pictures reliably. Very few people have “stable” hands for not moving the camera during exposure times longer than 1/60. Make sure that you do not move the camera locked on tripod when you press the shutter button. We recommend to use camera timer for shooting.

When you set sensitivity manually, select ISO100, or ISO200 in bright light. For dim light such as candlelight, select ISO3200, ISO6400 or higher, if the camera allows this. There is very little noise in the image when shooting in bright light. In dim light, when you increase ISO_speed to be able to shoot, but do not be surprised of speckles or noise in the image. Currently available cameras have some noise at high ISO_speed beyond ISO800, which is normal. At high ISO_number, the picture looses some details, too. However, camera manufacturers are continuously striving to reduce this noise.

Picture size is controlled by the operator. We suggest a reasonable size of 3072x2040pixels or 2400x1600pixels, or medium-size option for picture size. This gives reasonable picture quality on 1900x1024pixels computer screen and also on 4x6inches paper. Digital SLRs offer more choices for picture size, better sensitivity and less speckles in low light.

If the picture is sharp, do not be deceived if it is a little bit either darker or lighter. Anybody can fix this easily by computer, using one of the image viewers built in the modern operating systems, either Windows or MAC OS.

Portability and good image quality made today’s digital PS increasingly popular among the amateurs and professionals alike. The continuing progress in electronic technology made digital PS better at affordable prices, with increasingly better image quality.

We recommend several cameras from the Top 100 Best Sellers in Point-and-Shoot digital cameras:

Compact System Cameras released recently on the market by several companies such as Olympus, Sony and Nikon are digital PS cameras with lens-changing capabilities. We recommend Nikon 1 V1 10.1MP HD Digital Compact Camera System with 10-30mm VR 1 NIKKOR Lens.

We recommend several Compact System cameras from the Top 100 Best Sellers:


 

Digital SLR camera as you see in the left hand side of Digital Cameras Schematic, is a modern version of the film SLR camera. It has a reflex mirror and a pentaprism for directing the image from the lens toward the viewfinder. Digital SLR Cutaway schematic gives you 3D perspective of digital SLR camera. There are two main advantages of digital SLR camera over digital PS camera: (i) the lens can be changed and (ii) you always see in the viewfinder the image made by the lens attached to camera, regardless of the lens type.

You see below Canon EOS Rebel T3i, 18MP CMOS Digital SLR Camera with EF-S 18-55mm f/3.5-5.6 IS Lens, which is one of the most popular digital SLR cameras on the market. We also recommend this camera to our visitors.

A digital SLR camera diagram is shown in Digital Cameras Schematic at left hand side and also in Digital SLR Cutaway schematic. In the pointing position, the reflex mirror directs the image to a pentaprism and further to the viewfinder. A smaller secondary mirror, solidly attached to the reflex mirror and behind it, reflects the rays going through the main mirror toward the auto focus sensor located on the bottom side of the camera. Before pressing the shutter button, the operator defines the shooting area by looking through the viewfinder. When the operator presses gently the shutter button, the camera microcontroller adjusts the lens for the best sharpness using a sophisticated system containing an array of sensors and additional optics. Digital SLR allows the operator to set the best sharpness as explained above, either in the image center or off the center in one of the focusing points selected by photographer. The number and the position of image focusing points depends on camera manufacturer. Read carefully your camera manual for details. The same microcontroller adjusts also f/number and eventually the shutter speed for the best exposure for the selected ISO_number.

Shutter speed is computed by the microcontroller using the signals from the light metering system measuring the luminous flux of the image in up to 252 points. Pressing the shutter button beyond halfway position, the main mirror flips upwards for covering the pentaprism, thus preventing the ambient light from outside the camera to penetrate into the mirror box area. Now, the light from the lens hits the image sensor and the microcontroller opens up the shutter during the shutter speed time set either by the operator, or computed by the camera microcontroller, based on selected ISO_number and on the light metering. For selection of ISO_speed, follow the same hints as mentioned in digital PS. Digital SLRs have more choices for ISO_speed selection either in bright light, or in dim light. Select ISO100 or less in bright light. For dim light such as from candle, you can select ISO6400 or more, with some loss in image details. If you shoot a static scene in dim light, use a tripod and select ISO100 for preserving image details and for minimum noise. The pictures taken in bright light are practically free of speckles or noise. Camera manufacturers are constantly striving to reduce picture noise in dim light, which is not an easy task at all.
For shutter speed longer than 1/60, we recommend to use a stable tripod for obtaining consistently good quality pictures. Very few people have “stable” hands to not move the camera during longer exposure times. Make sure that you do not move the camera when you press the shutter button, even if the camera is locked on tripod.
We strongly suggest you to use also a tripod when you you use telephoto lenses with focal length longer than 85mm, even in bright light and when the shutter speed is slower than 1/250. The natural move of the hands is heavily amplified by the lens and can blur the image.

Digital Cameras Block Diagram shows the main elements of digital cameras and the functional links between them. The image sensor is a two-dimensional pattern of photosensitive elements or pixels for converting the image in electrical signal. Each pixel is converting the image across its area. More pixels across the image reveal more details of the image. An image sensor with a special color filter on top of it is used for color images. Today, all digital cameras have color image sensors containing between 6M pixels such as Nikon 1J1 and 36.3M pixels such as Nikon D800. The pixel count is very important, but is not the only parameter defining the image quality. Noise level of the image sensor and the Imaging Core have also important contribution to the picture quality.

The Imaging Core processes the signal from the image sensor. For clarity purposes, in Digital Cameras Block Diagram we show only Digital Image Processor and the Microcontroller as main components of the Imaging Core. In reality, the imaging core is very complex. Every digital camera manufacturer has its own Imaging Core, such as DIGIC of Canon and Expeed of Nikon. Briefly, the Imaging Core makes image processing, video processing and camera control. Image and video processing are strongly related to the characteristics of the image sensor. The Microcontroller performs multiple tasks such as reading ISO_number, exposure time and eventually f/number provided by operator through the user buttons. In automatic mode, the Microcontroller sets all exposure parameters. It performs also the best focus on the image sensor, triggers the flash unit, opens the shutter, saves the picture to the flash card and sends the picture to rear LCD.

Most of SLR cameras have also manual focus option. For best picture quality, we strongly suggest to use by default auto focus, which gives by far sharper images, works faster and gives more reliable results than manual focus. There are also rare situations, such as shooting through chain-link fence, when auto focus will focus on fence, which is closer to the camera than the targeted subject.

We recommend several cameras from the Top 100 Best Sellers in Digital SLR Cameras:

There are several types of flash memory cards for storing pictures of digital cameras, such as secure digital (SD, SDHC, SDXC), compact flash (CF), memory stick and MultiMedia Card (MMC). Always you need one to three spare flash memory cards for your camera. Three elements are important for flash memory cards: (i) mechanical compatibility, (ii) capacity expressed in GB, and (iii) speed. With so many flash card options available on the market, the best advice is to look at the camera manual to see the suggested flash memory cards for your camera. We recommend to choose the largest capacity supported by your camera, and fast enough to accommodate the camera transfer rate. Below are our recommended flash memory cards. For more options, follow the link.

Flash card management is totally at user’s choice. The user can select the picture size saved by the camera ranging from 720x480pixels, up to 6144x4912pixels. Obviously, larger image size gives more details, but less pictures can be stored on the flash memory card. It is always a tradeoff between the picture details and the number of stored pictures on the flash memory card. We suggest a reasonable image size of 3072x2040pixels or 2400x1600pixels, giving good picture quality on 1900x1024pixels on computer screen and also on 4x6inches paper. Typically, the digital cameras store the pictures in compressed .jpg format, widely accepted by most computers and Internet applications. All digital SLRs can store pictures also in RAW image format, to avoid compression artifacts associated with .jpg compression. Be sure that your camera was set to store the pictures in .jpg format, for efficient use of your flash memory card, and for easy transfer to your computer. Picture files in RAW format are used at professional level. They are very big, take a lot of space on your flash card, and need a camera manufacturer software for transferring them to your computer.

All digital cameras are provided with USB connection for transferring the pictures either to a computer, or to an iPad. Be aware that USB transfer consumes significant amount of power from the battery. Our suggestion is for using a flah memory card reader connected to a computer, which does not affect at all camera battery life.
When the scene is not sufficiently lit for taking a good picture, the microcontroller triggers either the built-in flash lamp, or the external flash lamp, if enabled by operator.

By default, the digital cameras keep ON the rear LCD for a limited time, for preserving the battery life. The ON time is set to default value in factory before shipping the camera, but it can be changed anytime by the user within large limits. We recommend 1s selection.

Many digital photo cameras have output for video signal, which allows to see the pictures on TV. Be aware that the available TV signal at the camera output must match the TV standards of your geographic region, such as NTSC for North-America, PAL and SECAM for Europe.

The high speed connection according to IEEE 1394 standard is optional for some digital photo cameras, but is always present in camcorders.

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Posted in Digital Camera

Lenses

Lenses for Digital Cameras

ver. 1
 
The photographer’s skill goes through the lens. The lens makes the image of the subject on the image sensor, ideally as the photographer sees with his eyes. Lens manufacturers work very hard to release new lens models with lower geometric distortions, better image clarity and image stabilization features at continuously decreasing price. Lens importance is obvious. This article highlights some basic aspects of camera lenses for using them better and recommends the best lenses for major subject categories.
The lenses made by major digital SLR manufacturers such as Canon and Nikon fit all their respective cameras. Check carefully the lens compatibility with your camera when buying lenses from third-party manufacturers such as Sigma and Tamron or others; some features such as auto focus or image stabilization might not work if the lens is not properly selected. Several aspects related to lenses will be highlighted further.

Crop factor is the number showing the ratio between the diagonal of 35mm film format and the diagonal of a particular image sensor. Full-frame image sensor collects the entire image of the lens designed for 35mm film camera; therefore the sensor gets the entire light collected by the lens, as you see in Cropped Images schematic. Follow the link of the image for more details. With a full frame camera, you expect the best outcome in angle of view and also in picture details. For full-frame sensor, camera sensitivity is limited only by the image sensor’s technology for a given lens. We recommend the best wide angle lenses for digital SLR:

APS-C image sensor of Canon has 25.1mm×16.7mm size, aspect ratio 3:2 and crop factor 1.6. APS-C is encountered in Canon EOS Rebel T3i 18 MP CMOS Digital SLR Camera and DIGIC 4 Imaging with EF-S 18-55mm f/3.5-5.6 IS Lens and also in other very successful digital SLR cameras, such as Canon EOS Rebel T4i 18.0MP CMOS Digital Camera. With its 18MP pixel count at relatively small size, the sensor reveals very well fine details of the image, as you can see in the sample image below. You can see more images if you follow the link of the image.
 

There are multiple aspects for taking into account at lenses for digital SLR and the image sensor of camera. Lenses for digital SLR must fit mechanically and eventually electrically as much as possible of digital SLR camera models of the same brand, from the lowest cost up to high-end units. Technical progress of digital SLR cameras could compromise sometimes this compatibility. An obvious example is for image stabilization lenses. They do image stabilization with new digital SLR cameras, but cannot perform this function with several years old digital SLRs, because the camera does not support this feature. There are also major differences between camera grades coming from the combination between image sensor and digital image controller. Smaller-size image sensor at lower cost crops from lens image the central part with inherent loss in sensitivity or in ISO_number. Full-frame image sensor allows the same angle of view like 35mm film camera by capturing the entire image from the lens. APS-H is an older version of image sensor with crop factor 1.3. It is encountered in products such as Canon EOS 1D Mark IV 16.1MP CMOS Digital SLR Camera with 3-Inch LCD and 1080p HD Video. However, you should keep in mind that the image sensor might see less from the image than you see through the viewfinder. Lower the crop factor, less image area covers the image sensor. The picture always shows what the image sensor has on its surface. We recommend the best lenses for APS-C sensors:

Focal Length defines the size of the viewing angle of the lens. Lenses with smaller focal length have larger viewing angle and gets less details of the scene. When using a short focal length, you appear far from the scene. Lenses with longer focal length have smaller viewing angle, but you get more details from the scene. When using a long focal length, the scene seems to be closer to you. Follow the link of the image for more examples.

The schematic Focal Length Comparison gives you an idea about the pictures of the same subject shot with two lenses with very large difference between their focal length. Currently available focal length covers a broad range from 10mm to 800mm. Lenses can have either fixed focal length or can have variable focal length or “zoom” within a certain range to expand part of the scene. Generally, fixed focal length lenses give pictures with more details and less distortions than the zoom lenses. With a zoom lens, you can select quickly just part of the scene without changing the lens or the the distance from camera and the scene. With a zoom lens, you just increase the focal length of the lens until you reach the desired detail, of course limited by maximum focal length of the lens. This can be very useful in many situations when you cannot go close to the scene as much as you wish. However, the “default” lens of the camera is subject to the operator’s choice. For most of the situations, we recommend telephoto zoom lenses with focal length spanning the range from 50mm up to 250mm, which can be eventually your default lens. Below we recommend some of the Best Seller Telephoto Lenses:


 

Diaphragm or Aperture or f/# as marked on the lens barrel, controls the light flux through the lens and also selects the depth of field. Smaller f/number such as f/5.6 gives a clear image within a small depth of field, providing the best sharpness of the lens. Larger f/number such as f/8 gives larger depth of field, but with some loss in details. It is only physics behind this. Image sharpness as explained above depends on the lens design and on the manufacturing technology. Camera lenses is a very competitive market. Certainly, lens price is strongly bonded to its features.

Image Focusing and Exposure tasks are preferable to be transferred to digital cameras. The digital SLR cameras have very sophisticated methods to measure the light. The diagram Light Metering Zones shows the light metering zones used by major digital SLR camera manufacturers such as Nikon and Canon. For most cases, auto focus does a better job than any operator unless special effects such as shooting a scene through a chain-link fence are targeted through manual settings.

Image sharpness as explained above assumes neither camera shake, nor subject shakes when shooting, picture size selection on camera is either medium or large, and there is no zooming when viewing the picture on 1920x1000pixels LCD monitor. Briefly, blur in digital images comes either from shooting conditions, or from electronic conditions such as storing and viewing. Some comments on image blur from shooting conditions can be helpful.

Image sharpness as mentioned above assumes neither camera shake, nor subject shake when shooting, picture size selection on camera as medium or large, and no zooming when viewing the picture on 1920x1000pixels LCD monitor. Blur in digital images comes either from shooting conditions, or from electronic conditions such as size of picture file and viewing the picture on computer screen, but not on TV. Some comments on image blur from shooting conditions can be helpful.

In the schematic Blurred Image Cases, the top row shows on the left hand side an image improperly focused on far field, behind the subject, which is in foreground. The focused picture is beside the subject. The middle row shows on the left hand side the situation when the camera moves during shooting: everything in image is blurred. Beside it is the correct picture. In the picture on the bottom row, left hand side, the subject is moving during shooting: it appears blurred, compared with the clear surrounding. In the picture beside it, the subject does not move during shooting and the picture appears clear everywhere. Follow the link of the schematic for more examples.
Hint: Improve your photographic skills by analyzing your bad pictures. The examples above refer only to blurred pictures, but can be other shooting situations such as improper lighting, exposure, framing, to name just a few which will be discussed in later articles.

Image stabilization is a very interesting feature, almost standard for camcorders. It provides sharp image even if the camera shakes for different reasons. This feature is spreads in more lenses for digital SLR.

We put together the features encountered in all lenses for digital SLR cameras, from the simplest lenses, up to most advanced lenses with image stabilization. Now you have a better idea about their features and how different settings can affect picture performance. We strongly encourage you to read all articles. We keep posting articles for helping you shooting better pictures.

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