The lens and shutter are attached to a lens-board which is connected to the body of the camera by a light-tight folding bellows.
When the camera is fully unfolded it provides the correct focus distance from the film.
The typical amateur camera of the early 20th Century made various "postcard" sized negatives around 4" × 5".
The use of folding cameras declined in the late 1930s with advances in lens technology allowing superior enlargement, high quality images on smaller negatives, and shorter distances between the lens and the film.
35mm film made small-sized cameras practical without using bellows.