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.

Tagged with: , , , , ,
Posted in Lenses