What is a Viewfinder?

It is not uncommon for a camera to have two viewfinders

A viewfinder is device on a camera, consisting of a lens system and sometimes a ground-glass screen, enabling the user to see what will be included in his photograph. It  is the preview window on a camera that is used to frame, focus and take the picture. On analog cameras, the viewfinder is an eye-sized window that must be pressed against the face to compose and focus the photo. Point-and-shoot digital cameras use small LCD screens that are viewed several inches from the eyes.

A viewfinder for Horseman SW cameras.
Professional photographers generally prefer a viewfinder for taking pictures. It blocks out surrounding distractions and lets them focus on framing the picture. In addition, the LCD screen can become very washed out in bright sunlight, making it almost impossible to frame the picture.

Digital SLRs and Prosumer Cameras Using optical lenses or a tiny microdisplay, digital SLR (DSLR) cameras employ the eye-sized viewfinder for taking pictures and an LCD screen for viewing the results. On some DSLRs, both viewfinder and LCD screen can be used for taking pictures. See DSLR.

Prosumer cameras have fixed lenses like point-and-shoot cameras, but they also have manual focus, aperture and shutter speed settings like DSLRs. Prosumer cameras generally have both a viewfinder and LCD screen for taking and reviewing pictures

Most viewfinders are separate, and suffer parallax, while the more complex 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 sync with its lens, one exception being rangefinder cameras.

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 two main advantages; it consumes no power, and it has "full resolution" (i.e. the resolution of the photographer's eye). An electronic viewfinder is a CRT, LCD or OLED based display device, though the former is rarely used today due to size and weight. In addition to its primary purpose, an electronic viewfinder can be used to replay previously captured material, and as an on-screen display to browse through menus.

It is not uncommon for a camera to have two viewfinders. For example, 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, and due to a rubber eyepiece it can be viewed perfectly even in bright light. The second viewfinder would be larger, of a higher resolution, and may be mounted on the side of the camera. 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.

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