Lenses and Focal Lengths
If you ask most photographers what they believe to be their most critical piece of photographic equipment, they would 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 world onto the sensor. The NEX-6, as a mirrorless camera that depends upon an interchangeable lens system, 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 scene (the ability to deliver great highlights and shadows). Most lenses now routinely 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 first consideration of the photographer: lens focal length, which determines the angle of view delivered through the lens. Lenses are typically divided into three or four groups, depending on the field of view they cover.
Wide-angle lenses cover a field of view from around 110 degrees to about 60 degrees (Figure 2.2). 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 30mm or smaller could be considered wide.
Figure 2.2. The 16mm lens setting provides a wide view of the scene but little detail of distant objects.
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 (Figure 2.3). 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 2.3. When you are shooting in tight spaces or want to exaggerate attractive lines, a wide-angle lens helps capture more of the scene.
A normal lens has a field of view that is about 45 degrees and delivers approximately the same view as the human eye (not in angle of view but in size and perspective of subjects). The perspective is 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 NEX-6 and its cropped sensor, it is more in the neighborhood of a 35mm lens (Figure 2.4).
Figure 2.4. Long considered the “normal” lens for 35mm photography, the 50mm focal length can be considered somewhat of a telephoto lens on the NEX-6 because it has the same angle of view and magnification as a 75mm lens on a 35mm camera body.
Normal focal length lenses are useful for photographing people, architecture, and most other general photographic subjects. They have very little distortion and offer a moderate range of depth of field (Figure 2.5).
Figure 2.5. Normal lenses are handy when photographing in the city, offering you the ability to quickly move from street photography to architecturural photography.
Most longer focal length lenses are referred to as telephoto lenses. They can range in length from 100mm 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 greatly reduced (Figure 2.6). You will also find that you can achieve a much narrower depth of field. They also demonstrate something called distance compression, which means they make objects at different distances appear to be much closer together than they really are.
Figure 2.6. The telephoto lens helped me get a tighter crop on West Texas’s downtown.
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 (Figure 2.7)—and a very narrow depth of field when shot at their widest apertures.
Figure 2.7. The longer the focal length, the more compressed the distance between foreground and background objects will be.
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. (We’ll discuss all this in more detail in later chapters.)
The NEX-6 can be purchased with the body only, but many folks will purchase it with a kit lens, the E-Mount 16–50mm f/3.5–5.6. Another great lens option for the NEX-6 is the E-Mount 18–200mm f/3.5–6.3 lens. Although pricier than the 16–50mm, the 18–200mm is a great all-around lens that provides a range of focal lengths, from the very wide to the medium telephoto. Combine that with great Optical SteadyShot image stabilization technology and you have what I like to call the perfect vacation lens. Unfortunately, it is not available as a kit lens at the moment, but you should definitely consider it if you are thinking of adding a new lens to your camera bag.