B is for Bellows
Many older cameras possess bellows, an expandable dark chamber connecting the lens of the camera body to the camera body where the film is.
By being expandable, the position of the lens relative to the film can be changed to focus the image.
More practically, being able to move the lens means that a camera can be folded up to a smaller size, therefore making it more convenient to carry.
See the other 25 letters of the 2020 A to Z challenge from Animal’s Place by clicking here! All about how cameras work!