Viewfinder

Viewfinder is what the photographer looks through to compose, and in many cases to focus, the picture. Most viewfinders are separate, and suffer parallax, while the more sophisticated single-lens-reflex camera lets the viewfinder use the main optical system.

Viewfinders are used in many cameras of different types: still and movie, film, analog and digital. A zoom camera usually zooms its finder in synch with its lens.

Viewfinders can be optical or electronic. An optical viewfinder is simply a reversed telescope mounted to see what the camera will see. Its drawbacks are many, but it has one main advantage: it consumes no power. An electronic viewfinder is a CRT, LCD or OLED based display device.

In addition to its primary purpose, an electronic viewfinder can be used to replay previously captured material and usually has an on-screen-display. It is not uncommon for a camera to have two viewfinders. Here are two examples:

• A digital still camera may have an optical viewfinder and an electronic one. The latter can be used to replay previously captured material, has an on-screen display, and can be switched off to save power.
  
  
• A camcorder may have two viewfinders, both electronic. The first is viewed through a magnifying eyepiece. The second viewfinder is a mounted on the side of the camera and projected on a CRT or LCD-screen. Because it consumes more power, a method is often provided to turn it off to save energy.

Some special purpose cameras do not have viewfinders at all. These are, for example, web cameras and video surveillance cameras. They use external monitors as their viewfinders.