Photographic lens

A photographic lens (or more correctly, objective) is a lens used for a camera. It may be fixed to the camera body, or interchangeable. There will usually be an aperture selection mechanism for adjusting the amount of light through the lens, and a focussing mechanism. Depending on type of camera, there may also be an integrated shutter.

The maximum aperture opening will normally be specified, as the f-number. The lower the number, the more light is admitted through the lens. On lenses for SLR cameras, there is usually an auto mechanism, where by the aperture is held fully open while focusing, but closes to its preset value when an image is taken.

The most important characteristic is the focal length, which is usually measurd in mm (cm up to around 1960), and which places the lens in one of three categories:

• Normal lens
• Telephoto lens
• Wide-angle lens

Some notable photographic optical lens designs are:

• Cooke Triplet
• Zeiss Tessar
• Zeiss Sonnar
• Zeiss Planar
• Double-Gauss
• Angenieux retrofocus

See also:

• Lens