In photography, a bellows is the pleated expandable part of a camera, usually a large

Large format

Large format refers to any imaging format of 4×5 inches or larger. Large format is larger than "medium format", the 6×6 cm or 6×9 cm size of Hasselblad, Rollei, Kowa, Pentax etc cameras , and much larger than the 24×36 mm frame of 35 mm format.The main advantage...

 or medium format camera

Camera

A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...

, to allow the lens to be moved with respect to the focal plane for focusing.

The bellows provides a flexible dark enclosure (the camera obscura

Camera obscura

The camera obscura is an optical device that projects an image of its surroundings on a screen. It is used in drawing and for entertainment, and was one of the inventions that led to photography. The device consists of a box or room with a hole in one side...

) between the film plate and the lens. In some cameras, the photographer can change the angle of the film plate with respect to the optical axis of the lens, providing alterations of perspective distortion and of the object plane of focus.

There are 2 common kinds of camera bellows:

• bag bellows, normally used with a lens of short focal length
• accordion bellows, with a much longer range of extension.

For large format cameras

View camera

The view camera is a type of camera first developed in the era of the Daguerreotype and still in use today, though with many refinements. It comprises a flexible bellows which forms a light-tight seal between two adjustable standards, one of which holds a lens, and the other a viewfinder or a...

, “double extension” refers to bellows that extend to a length equal to about twice the focal length of a standard lens, e.g. 300 mm for the 4×5 inch format. “Triple extension” for the same format indicates bellows extension of 450 to 500 mm.

Bellows on a camera can be used to correct distortion in a photograph. For example, when shooting a scene with strong vertical elements which are truly parallel to each other, some camera systems would tend to curve these elements and make them appear in the resulting photograph to NOT be parallel. Use of a bellows-based camera can ensure that parallel elements in a scene remain parallel in the final photograph.