If you ask most photographers what they believe to be their most critical piece of photographic equipment, they would undoubtedly tell you that it’s their lens (also referred to as “glass”). The technology and engineering that goes into your camera is a marvel, but it isn’t worth much if it can’t get the light from the outside onto the sensor. Most photographers will happily put their resources into purchasing highquality lenses before they get a new camera body, since lenses can be passed on from one camera to the next and are a huge factor in the overall quality of the image.
The 7D, as a digital single lens refl ex (DSLR) camera, uses the lens for a multitude of tasks, from focusing on a subject, to metering a scene, to delivering and focusing the light onto the camera sensor. The lens is also responsible for the amount of the scene that will be captured (the frame). With all of this riding on the lens, let’s take a more in-depth look at the camera’s eye on the world.
Lenses are composed of optical glass that is both concave and convex in shape. The alignment of the glass elements is designed to focus the light coming in from the front of the lens onto the camera sensor. The amount of light that enters the camera is also controlled by the lens, the size of the glass elements, and the aperture mechanism within the lens housing. The quality of the glass used in the lens will also have a direct effect on how well the lens can resolve details and the contrast of the image (the ability to deliver great highlights and shadows). Most lenses now include things like the autofocus motor and, in some cases, an image-stabilization mechanism.
There is one other aspect of the camera lens that is often the fi rst consideration of the photographer: lens length. Lenses are typically divided into three or four groups depending on the fi eld of view they deliver.
Wide-angle lenses cover a fi eld of view from around 110 degrees to about 60 degrees (Figure 2.5). There is a tendency to get some distortion in your image when using extremely wide-angle lenses. This will be apparent toward the outer edges of the frame. As for which lenses would be considered wide angle, anything 35mm or smaller could be considered wide.
Wide-angle lenses can display a large depth of fi eld, which allows you to keep the foreground and background in sharp focus. This makes them very useful for landscape photography. They also work well in tight spaces, such as indoors, where there isn’t much elbow room available. They can also be handy for large group shots but, due to the amount of distortion, not so great for close-up portrait work (Figure 2.6).
A normal lens has a fi eld of view that is about 45 degrees and delivers approximately the same view as the human eye. The perspective is very natural and there is little distortion in objects. A normal lens will have a focal length between 35 and 80mm. (Figure 2.7).
Normal focal length lenses are useful for photographing people and architecture, and for most other general photographic needs. They have very little distortion and offer a moderate range of depth of fi eld (Figure 2.8).
Most longer focal length lenses are referred to as telephoto lenses. They can range in length from 135mm up to 800mm or longer and have a fi eld of view that is about 35 degrees or smaller. These lenses have the ability to greatly magnify the scene, allowing you to capture details of distant objects, but the angle of view is greatly reduced (Figure 2.9).
Telephoto lenses are most useful for sports photography or any application where you just need to get closer to your subject. They can have a compressing effect— making objects look closer together than they actually are—and a very narrow depth of fi eld when shot at their widest apertures.