Camera Lenses
Most film or digital SLR cameras allow you to interchange lenses to give you the tactical advantage of having the right one for the right situation. So which is the right lens to use? Camera companies are constantly coming out with new and improved models, so this article will help describe the different types that are available, rather than specific brands or models.
Lenses are classified by their focal length, or in the case of zoom lenses, their range of focal lengths, and their maximum aperture size. A focal length of 50mm is considered normal because it is similar to what the human eye sees; therefore a 100mm focal length zooms in an object by two times, a 500mm focal length equals 10x magnification, etc. When going less than 50mm, every time the focal length halves, it makes things twice as small. Therefore, a 25mm focal length is .5 magnifications or 2 times as small, 12mm focal length is .25 magnification or 4 times as small, etc. Therefore, the type of lens indicates its relation to the human eye. Telephoto lenses zoom in on an object, normal lenses are the same as the human eye, and wide angle lenses make things smaller than the eye would see them.
Note: Digital cameras have a smaller light sensor than a 35mm film camera. Therefore, if you are shooting with a digital camera, you need to multiply the focal length by 1.5. Some cameras may be different, so check your specific owner's manual, but most are going to be this way. What this means is that a focal length of 50mm is going to be the same as 75mm or 1.5 times magnification, and around 33mm will be the same as a human's eye.
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Wide Angle Lens
The wide angle lens is useful for two main reasons. First, it allows a photographer to get more into the picture without having to back up, which could be several miles if the subject is very large. Second, it helps create a sense of depth in the picture by making the things in the foreground larger, and the things in the background smaller.
Because of the change in depth perception, vertical lines that aren't parallel to the camera's back might look like they are leaning toward or away from each other so it's important to keep the camera parallel with vertical objects like trees and poles. To change the composition, move the camera up or down, but don't tilt it.
Normal Lens
A focal length of 50mm (33mm for most digital cameras) is considered normal because it represents a scene with the approximate angle that the human eye can see. Normal lenses are good for still life, landscapes, trees, flowers, and images where the subject is interesting by its own without the need for optical enhancements.
Telephoto Lens
A telephoto lens is any lens with a focal length that is greater than 50mm for film and 33mm for digital cameras. Typical telephoto lenses range from 200-1000mm and different focal lengths are useful for different situations. To fill a bird in the frame at about 15-20 feet away, a 500mm telephoto lens may be required (300-400mm for digital). To shoot a larger animal such as a deer or a moose, only 200-300mm (150-200mm for digital) is needed.
Depending on the size of the lens, a tripod is probably needed to prevent the image from being blurred, which when added to the weight of the rest of the photographer's gear can be bulky, heavy, and somewhat difficult to pack around. In addition to the tripod, a cable release, self-timer, or remote shutter release should be used to prevent camera shake.
Beyond zooming in on a far away object, a telephoto lens makes objects seem much closer to each other than they really are. This phenomenon has been used in hunting magazines to make the animals look a lot bigger than normal. The animal is propped up from behind so that the prop doesn't show up in the picture. Then the hunter stands far back from the animal, but positions himself so that it looks like he is holding up the animal's head. The photographer stands far away at just the right angle so that everything is in line. When the picture is shot with a telephoto lens, the animal looks a lot larger next to the hunter because it is much closer, but both the hunter and animal appear to be right next to each other in the photo.
Macro Lens
Macro lenses allow a photographer to focus on an object much closer than normal. They are great for small objects such as flowers and insects, but they can also be useful with distant scenes especially with pictures that contain a lot of flat surfaces. They have small maximum apertures and fixed focal lengths. While they may be the best at what they do, other lenses can be used to do just about everything that a macro lens would be used for.
Prime Lens
This is a lens with a fixed focal length. The most common is a 50mm lens because it represents the normal view from the naked eye; however, keep in mind that current digital cameras have a 1.5 focal length modifier, which means that a 50mm lens is the same as 75mm (or 1.5x magnification) on a 35mm film camera. A 50mm prime lens is currently about $120. There are other focal lengths available from ultra-wide to telephoto, which tend to bump up the price dramatically. There are two advantages that prime lenses have over zoom lenses. First, they are usually less expensive than their zoom counterparts because they are easier to manufacture. It's also easier to make the glass perfectly sharp all of the way to the edge, which allows the manufacturer to make a larger aperture. Larger apertures let in more light and decrease the depth of field visible in an image, which is perfect for indoor shots, concerts, and portraits without needing to use the flash as much.
Zoom Lens
A zoom lens can vary in focal length. These are very common today and are much more convenient than carrying around a bunch of different lenses at different focal lengths. It used to be that fixed focal length lenses (also called prime lenses) were preferred because zoom lenses couldn't be trusted, whether real or perceived, to be perfect at their entire range of focal lengths, but this is no longer the case.
Common zoom lenses focus on being either wide angle or telephoto. The wide angle zoom lenses tend to range from 18-70mm (27-135mm for digital), but there are a few with a wider range of focal lengths. The telephoto zoom lenses usually start where the wide angle left off. These tend to range from 55mm to 400mm, but few fill that entire range.
Other Lenses
There are others available such as perspective control lenses, APO, and teleconverters that help in specific situations. Chances are that if you need one of these, then you already know what they are.
Which lenses do you need?
This really depends on the individual photographer. Nature and wildlife photographers should be able to shoot from wide angle to telephoto; however, remember that you'll probably be hiking around with your gear so keep that in mind. Other types of photographers will need lenses specific to their situation and individual style.
About the Author
Brian Broderick (http://www.brianbroderick.com) is a semi-pro nature photographer and the creator of The Lens Flare. His hobbies include hiking, skiing, and computer graphics, and is currently a web programmer.
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