If you ask most professional photographers what they believe to be their most critical piece of photographic equipment, they will undoubtedly tell you that it is their lens. The technology and engineering that goes into your camera is a marvel, but it isn’t worth a darn if it can’t get the light from the outside onto the sensor. The D7000, as a digital single lens reflex (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 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 routinely include things like the autofocus motor and, in some cases, a vibration reduction mechanism. If you bought the Nikon D7000 kit lens, then your 18–105mm lens is equipped with both autofocus as well as vibration reduction.
There is one other aspect of the camera lens that is often the first consideration of the photographer: lens length. Lenses are typically divided into three or four groups depending on the field of view they deliver.
Wide-angle lenses cover a field of view from around 110 degrees to about 60 degrees (Figure 2.6). There is also 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 field, 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 be handy for large group shots but aren’t so great for close-up portrait work, due to the amount of distortion.
A normal lens has a field of view that is about 45 degrees and delivers approximately the same view as the human eye. The perspective feels very natural, and there is little distortion in objects. The normal lens for full-frame and 35mm cameras is the 50mm lens, but for the D7000 it is more in the neighborhood of a 35mm lens. Often I’ll use a 50mm or an 85mm for street photography (Figure 2.7).
Long viewed as the “normal” lens for 35mm photography, the 50mm focal length can be considered somewhat of a telephoto lens on the D7000 because it has the same angle of view and magnification as an 80mm lens on a 35mm camera body. I find it to be the perfect lens to use for many portraits.
Normal focal length lenses are useful for photographing people and architecture and most other general photographic purposes. They have very little distortion and offer a moderate range of depth of field (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 field 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 sharply reduced. You will also find that you can achieve a much narrower depth of field. They suffer from something called distance compression, which means they make objects at different distances appear to be much closer together than they really are (Figure 2.9).
Telephoto lenses are most useful for wildlife and 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 field when shot at their widest apertures.
A zoom lens is a great compromise to carrying a bunch of single focal-length lenses (also referred to as prime lenses). They can cover a wide range of focal lengths because of the configuration of their optics. However, because it takes more optical elements to capture a scene at different focal lengths, the light must pass through more glass on its way to the image sensor. The more glass, the lower the quality of the image sharpness. The other sacrifice that is made is in aperture. Zoom lenses typically have smaller maximum apertures than prime lenses, which means they cannot achieve a narrow depth of field or work in lower light levels without the assistance of image stabilization, a tripod, or higher ISO settings.
The D7000 can be purchased with the body only, but many folks will purchase it with a kit lens. The most common kit lens is the 18–105mm VR f/3.5–5.6. Throughout the book, I will occasionally make reference to lenses that are wider or more telephoto than these, because I have a multitude of lenses that I use for my photography. This doesn’t mean that you have to run out and purchase more lenses. It just means that if you do this long enough, you are sure to accumulate additional lenses that will expand your ability to be even more creative with your photography.