When you are taking a picture, you want to know with enough precision what will appear. This is called framing and is the role of the viewfinder.
There are different kinds of viewfinder:
- Optical finder or direct vision finder: It is an optical device, like a tiny telescope that you peer through at the scene. On the simplest ones, found on most low cost cameras, (i) the view angle is fixed, (ii) the picture frame is defined by the finder's borders and (iii) there is no focusing assistance. These limitations are respectively overcome in the following variants:
- Zoom optical finder: Similar to the above, but with a zoom feature, so that the view through the viewfinder changes as you zoom the lens. This is mostly used on low cost cameras with a zoom lens and autofocus.
- Optical viewfinder with rangefinder: This is the combination of a simple optical viewfinder and a rangefinder. This gives a focusing assistance inside the viewfinder on some manual focus cameras. See rangefinder (device).
- Projected frame finder: A frame is visible in the finder to delineate the picture. On interchangeable lens cameras, the frame is switchable or there are multiple frames displayed at once.
- Reflex finder: See Reflex finder.
- Ground glass back: See Ground glass back.
- Electronic viewfinder (EVF): On digital cameras only. It is an LCD screen built inside the camera and observed through an eyepiece. It is usually found in big digital cameras having neither optical viewfinder nor reflex finder.
- LCD screen: On digital cameras only. It is a small LCD screen, placed on the back of the camera and sometimes orientable.
- Bright finder or brilliant finder: No longer in use. This was a small finder with a mirror inside. You looked through it from above, with the camera held on your chest or belly. The image was inverted left to right, and it was not really comfortable. It was used on inexpensive cameras until the 1950s.
- Frame finder: No longer in use. This was the simpler design, with no optics at all, consisting merely of framing devices that the user looks through to frame the scene they wanted to take. These types of viewers were present even on cameras which had conventional viewfinders, such as press cameras; they were called "sportsfinders" since they could be used to quickly frame action on a field. Typically, such a finder had two parts: a large wire frame that extended above or to the side of the camera, and a smaller frame that the user put their eye up to. It was sometimes built in the viewing hood of twin lens reflex cameras.