Viewfinder

Direct viewfinders are essentially miniature Galilean telescopes; the viewer's eye was placed at the back, and the scene viewed through the viewfinder optics. A declining minority of point and shoot cameras use them. Parallax error results from the viewfinder being offset from the lens axis, to point above and usually to one side of the lens. The error varies with distance, being negligible for distant scenes, and very large for close-ups. Viewfinders often show lines to indicate the edge of the region which would be included in the photograph.

Some sophisticated 20th century cameras with direct viewfinders had coincidence (split-image) rangefinders, initially with separate windows from the viewfinder, later integrated with it; they were called rangefinder cameras. Cameras with interchangeable lenses had to indicate the field of view of each lens in the viewfinder; more usually, interchangeable viewfinders to match the lenses were used.

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  Leica IIIf viewfinder camera, 1951
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  German Tewe 35 mm to 200 mm zoom viewfinder
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  Early 21st century digicam with viewfinder

Simple reflecting viewfinders, known also as "brilliant finders", comprised a small forward-looking lens, a small mirror at 45° behind it, and a lens at the top; the user held the camera at waist level and looked down into the lens, where a small image could be seen. Such viewfinders were integrated into box cameras, and fitted to the side of folding cameras. These viewfinders were fitted to inexpensive cameras.

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  Hasselblad
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  Child's waist-view box camera
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  Mamiya 645 1000s waist level finder
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  Robot Royal III camera with Zeiss Ikon waist level viewfinder attachment

For many sports and press applications optical viewfinders gave too small an image and were inconvenient to use for scenes that were changing rapidly. For these purposes a simple arrangement of two wire rectangles, a smaller one nearer the eye and a larger one further away, was used, with no optics; the two rectangles were aligned so the smaller one was centred in the larger, and the larger rectangle would give an indication of what would be included. This was fast and convenient to use, but not particularly accurate; cameras with sportsfinders usually had optical viewfinders too.

A sportsfinder is sometimes known as an Albada finder. It is a "viewfinder used with a camera held at eye level; the field of view is enclosed by a white frame that is made to appear very distant by reflection from the rear surface of the objective lens".[3]

Using a TLR

Twin-lens reflex (TLR) cameras had a large lens above the taking lens, and a large mirror at 45°, projecting an image onto a ground glass screen viewable from above, with the camera at waist level. The viewfinder lens was of similar size and focal length to the taking lens, though the optical quality was less critical; the mirror was of similar size to the film. These cameras were relatively expensive; the Rolleiflex and cheaper sister Rolleicord were the pioneers. Both single- and twin-lens reflexes allowed focussing by adjusting the lens until the image was sharp.

Mamiya 645 1000s AE finder

Single-lens reflex (SLR) cameras viewed the scene through the taking lens. Early SLRs were plate cameras, with a mechanism to insert a mirror between the lens and the film which reflected the light upwards, where it could be seen at waist level on a ground glass screen. When ready to take the picture, the mirror was pivoted out of the way (without moving the camera). Later SLRs had a mechanism which flipped the mirror out of the way when the shutter button was pressed, followed immediately by the shutter opening. Instead of a waist-level arrangement, a prism was used to allow the camera to be held to the eye. The big advantage of the SLR was that any lens, or other optical device, could be used; the viewfinder always showed exactly the image that would be projected onto the film. The live preview feature of digital cameras share this advantage of the SLR, as they also show the image exactly as it will be recorded, with no additional optics or parallax error.