Differences in Telephoto Lenses
If you are taking pictures with a SLR, or single-lens reflex camera, you are able to change the lens attached to the camera based on the subjects of your picture. Telephoto lenses are camera lenses that are are used for zooming in on subjects. Medium telephoto lenses have focal lengths that run from 70mm to 135mm. Any lenses with a focal length longer the 135mm is referred to as a telephoto lens. Most telephoto lenses are used for taking pictures of portraits, sports and wildlife.
Focal Length
The zoom of a telephoto lens can vary largely from 70mm to 600mm or higher. Each time the focal length of the lens doubles, you zoom in twice as far. For example, a 400mm lens has twice the zooming power as a 200mm lens. Typically, the longer the focal length, the more expensive the lens will be. Also, some telephoto lenses are primes while others are zoom lenses. Prime lenses have only one focal length, such as a 400mm lens, while zoom lenses cover a range of focal lengths, such as a 100 to 400mm lens. In general, prime lenses offer a slightly higher image quality than zooms. However, for many people, the minor loss of quality is more than made up for by the flexibility a zoom lens offers. With a prime lens, you must physically move to change the composition of your photo. With a zoom lens, you can adjust the composition with a twist of the focal length ring.
Aperture
The aperture refers to how much light the lens allows to hit the camera's sensor. Lenses that have a wider aperture have smaller numbers and allow more light to hit the sensor. For example, a lens with a maximum aperture of 2.8 will allow more light to hit the sensor than a lens with a maximum aperture of 5.6. Having a wider aperture is especially helpful for shooting sports because more light allows you to use a faster shutter speed to freeze fast moving athletes, and indoor or night shots, because of the limited light in those situations. Some zoom telephoto lenses may have a range listed as the maximum aperture, such as 3.5 to 5.6. When a range is listed, the smallest number refers to the maximum aperture at the widest zoom, and the larger number refers to the maximum aperture at the tightest zoom.
Image Stabilization and Vibration Reduction
Telephoto lenses are generally the largest lenses and can weigh several pounds, so it can be hard to hold the camera perfectly steady when taking a picture. Image stabilization and vibration reduction are two technologies developed by Canon and Nikon, respectively, that minimize the blur caused by your hand shaking while taking the picture. These technologies make the lenses more expensive, but can be worth it for the improved photo quality. However, these technologies will not improve your photos if you are using a tripod, nor will it help freeze fast moving sports.
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