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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