This sounds like a process camera. It works just as you described. It can be use d for enlarging or reducing the original item which is held in the copyboard (gl ass covered frame). Some people use these as a basis for making a large format e nlarger by adding a light source to the back, negative holder in place of the gr ound glass, etc. If it is complete, the lens is most likely to be the most valua ble part of whole camera.