Telephoto Lens

You've probably heard that telephoto lenses are for enlarging distant subjects, but they're also a powerful artistic tool for affecting the look of your subject. They can normalize the size and distance difference between near and far objects, and can make the depth of field appear more shallow. Telephoto lenses are therefore useful not only for wildlife photography, but also for landscape photography.

Overview
A lens is generally considered to be "medium telephoto" when its focal length is greater than around 70 mm. However, many don't consider a lens a "full telephoto" lens until its focal length becomes greater than around 135 mm. This translates into an angle of view which is less than about 15° across your photo's widest dimension. On a compact camera with a 3-4X or greater zoom lens, telephoto is simply when you've fully zoomed in. However, some compact cameras might require a special adapter in order to achieve full telephoto.
Regardless, the key concept is this: the longer the focal length, the more you will tend to notice the unique effects of a telephoto lens.

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