Bellows (photography)

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In photography, a bellows is the pleated expandable part of a camera, usually a large or medium format camera, 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) 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, “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.