What you are showing is a bellows and a focusing rail For a 35 mm single lens reflex camera. Units like this were popular in the 1970s and 1980s for high magnification photography. The camera lens or an enlarger lens is mounted on the front of the bellows, and the focusing rail allows you to use various degrees of extension. Think of it as it continuously adjustable set of extension tubes!
Oftentimes these were used to make duplicate 35mm slides, and Nikon used to call these by various model numbers beginning with the prefix PB