Telephoto Lens
Lenses have different focal lengths. Normal lenses have a focal length of about 50mm. They are known as normal because they “see” as a human eye does. A telephoto lens has a focal length of 70mm or more, and it is used to bring the subjects closer, or magnify them.
A telephoto lens with a 200mm focal length magnifies the subject four times as much as a normal, 50mm lens. 400mm telephoto lenses have a magnification of 8x compared to a 50mm lens, and 2x compared to a 200mm lens.
If you are planning on buying a telephoto lens, be sure you have a tripod. And if your digital SLR camera isn’t equipped with sensor shift stabilization (body based stabilization), try to find a lens with built-in image stabilization (lens shift stabilization) to counteract camera shake, which is amplified the longer the focal length of the lens.