What is the difference between a telephoto lens and a zoom lens?

Question

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.

Update:
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.

Answer 1

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).

Answer 2

Technically 'Telephoto' means that the focal length [the mm] is longer than the lens is. In my experience, people in the photography world usually don't talk about it under that definition.

Most of the time people say 'Telephoto' they just mean 'zoomed in' or in other words 'high mm' or 'long focal length' As has been mentioned, Nikon seems to say that 85mm is the shortest focal length that they will call telephoto. I have seen people call anything above 50mm telephoto.

'Zoom' just means that it has a range of focal lengths. That range could be telephoto, it could be below telephoto, or it could range from below telephoto to above telephoto.

Here are a few examples:

A 300mm lens is a telephoto but is not a zoom because 300mm is high mm (in other words, 'long focal length' or 'zoomed in') but it does not cover a range of focal lengths. (You can only use that lens at 300mm, not 299mm or 472674mm) Insead, we call these lenses prime lenses. A prime lens does not cover a range of focal lengths, just one.

A 10-20mm lens is not a telephoto lens but is a zoom lens. It is not zoomed in at all. It has a short focal length, low mm. It's called wide angle. If you felt like it, you could shoot at 15mm when you feel jumpy and 16mm when you feel bumpy. You could not, however shoot at a high focal length as you could with the 300mm lens.

An 18mm lens is not a telephoto lens and it is also not a zoom lens because it has low mm and there is only one focal length. You'd call it a wide angle, prime lens.

An 18-200mm lens is a strange beast. It is a zoom lens but it can be considered both a wide angle (at 18mm) and a telephoto lens (at 200mm) because it's zoom range is so huge. You could shoot at 200mm and it's telephoto or you could shoot at 18mm and it's wide angle. In my experience if it is capable of telephoto, then you call it a telephoto. You'd then call it a telephoto zoom

So to talk about focal lengths:

It's either a wide angle lens (zoomed out) or a telephoto lens. (zoomed in)

And to talk about focal length range:

It's either a prime lens (only one focal length) or a zoom lens (range of focal lengths)

Answer 3

A zoom lens means the lens can change focal length via zooming, i.e. it is not a prime lens. A telephoto lens has a long focal length (I do not know if there is an official threshold to call a lens telephoto, but Nikon seems to start it at 85mm.

So, you can have a prime telephoto lens that is not a zoom, and you can have a wide angle zoom lens.

Answer 4

Zoom lens = can do this:

Telephoto lens = it can display stuff that are far away so big so that you can see them in detail.

See this:

• 
  taken with normal lens
• 
  taken with telephoto lens

_{Animation by Stefan-Xp from Wikimedia Commons, CC-BY-SA, both pics by Koyaanis Qatsi}