Lenses and Focal Length

The focal length of a lens tells is a measure of how much it magnifies things, and controls how much of a scene you can fit into the frame. Lenses generally fall into three groups:

If you can adjust the focal length of your lens it is called a zoom lens - when you "zoom-in" you are increasing the focal length. If the focal length is fixed then photographers call that a prime lens. Most compact cameras have a zoom lens because it's more convenient to have a range of focal lengths without having to carry around several different lenses and to keep changing them. Serious professional photographers tend to use prime lenses because they can be of higher quality.


Look at the pictures taken below with lenses of focal lengths varying from 12mm (very wide-angle) to 200mm (telephoto). I was standing in the same spot for each of the pictures, and they were taken within a few seconds of each other - although the sun went in after I took the first one. Concentrate on the car that's parked in the road (to the right of the For Sale sign) - you can barely even see it at 12mm, but you can clearly read the number plate at 200mm. Notice also that the house on the left of the first photo looks slightly stretched - this is the distortion I mentioned above when talking about wide-angle lenses.

12mm - very wide-angle (you can just about make out a car parked down the road)
28mm - a standard wide-angle lens for a 35mm or full-frame digital SLR
50mm - the "standard" lens for a 35mm or full-frame digital SLR camera
70mm - slight telephoto
200mm - zoomed in; it's an 06-reg Vauxhall Vectra!