SLR Photography Online

The "focal length" of a lens.

The focal length of a lens can be defined as the distance from a point within the lens to the film plane when the lens is focused on infinity. Focal lengths are normally stated in the metric system in millimeters. The "standard" lens supplied with most SLRs is 50 mm, roughly 2 inches.

Lenses that have shorter focal lengths than that of a standard lens have a greater angle of view. Ones with longer focal lengths take in a narrower angle of view.

Movie Requirements

Movie: Focal Lengths

Part 1: The lens extends as the focal length is increased (from 70mm to 210mm) by turning the zoom barrel.
Part 2: An example of a zoom increasing its focal length.

Depending on how close you need to be to your subject and how large your subject is, you will need different length lenses. A wide-angle lens (24-28mm) should be used when you have a large subject and compose the entire scene with a standard lens. A telephoto lens (100-500mm) is useful when you can't get close enough to your subject to fill the picture. A zoom lens's focal lengths can be changed over a range (for example: 28-80mm).

28mm Photo taken at 28mm.

50mm Photo taken at 50mm.

80mm Photo taken at 80mm.

135mm Photo taken at 135mm.

210mm Photo taken at 210mm.