What is the difference between a telephoto lens and a zoom lens?
Looking at the product page for Nikon lenses, I notice a distinction between telephoto lens and zoom lens.
What is the difference between the two? Why would I want one over the other? I wiki'd telephoto lens but remain confused about this distinction.
Please talk to me like I'm stupid. :) I am hoping for a completely lay explanation. In particular, I'd like to understand in what situations I'd use a telephoto lens, and in what (other) situations I'd use a zoom lens.
The focal length of a lens determines its field of view on your camera. If it has a long focal length, it has a narrow field of view, making the things in front of you appear large in the photograph. If it has a short focal length, it has a large field of view--it's a "wide angle" lens that takes in a large area, making objects appear small.
A "zoom lens" is a lens whose focal length can change. You twist the barrel, or push a switch on the camera, and it takes in a narrower or wider field of view, making objects appear bigger or smaller.
The term "telephoto lens" has a particular technical meaning in terms of lens design, but in common usage it refers to a lens with a long focal length.
A zoom lens could "zoom" from a short (wide-angle) to long ("telephoto") focal length, making things look bigger and closer as you zoom in. Or it could zoom from an extreme wide-angle to a moderate wide-angle, never coming close to a "telephoto" focal length. Or any other range of focal lengths.
So "zoom" = focal length you can change, and "telephoto" = long focal length. A lens can be one, or the other, or neither, or both.
The focal length is normally measured in millimeters (mm). A zoom lens will have two measurements, for example "18-200 mm" (a wide-angle to telephoto zoom). It zooms from a short focal length of 18 mm to a long focal length of 200 mm. A non-zoom lens, also called a "prime" lens, will have a single focal length, for example "135 mm" (a moderate telephoto).
Thank you for this excellent explanation. I still remain unclear; why one would purchase a pure telephoto lens? Comparing with zoom lens, it seems like a good zoom lens can often offer similarly large focal lengths as a pure telephoto lens.
a lens can be both a telephoto and a zoom. Also, non-zoom lenses ('prime' or 'fixed focal length' lenses) are often sharper and faster than zooms that cover the same focal length. The zooms on the other hand give you the convenience of being able to zoom as opposed to having to switch lenses.