Choosing the right telephoto lens for you comes down to what you are shooting, what camera brand you use, and your budget. Longer telephoto lenses over 300mm will typically be more expensive than lenses that fall in the 70-200mm range. A wildlife photographer or a sports photographer will probably get more use out of a 300mm lens than someone who is planning to use the lens for photographing live music or weddings. Make sure that the telephoto lens that you purchase will be compatible with your camera body, this is especially important when shopping for third-party lenses.