Dentists and opticians once used cameras like this for extreme close-ups of patients’ teeth and eyes. It’s a 35mm single lens reflex based on the Yashica FX-3 body but with an unusual lens surrounded by a ring flash. The shutter speed is fixed at 1/125 second; the lens is a 55mm f/4. There is no focusing scale but, as you turn what looks like a big, wide focusing ring, you are actually adjusting the magnification from 1:1, which records objects on film life-size, in 13 increments out to 1:10

 

Having chosen the degree of magnification needed for the subject, the camera is moved backwards and forwards to focus. A small bulb situated above the lens can be turned on to aid focusing. The film speed is set on a dial on the top plate. Flash output remains constant, but to maintain correct exposure, the aperture automatically closes down as the magnification is increased, and therefore the camera-to-subject distance is decreased. This method of setting smaller apertures 

at closer focusing distances also compensates for changes in depth of field.

 

The shutter is mechanical; the flash and bulb are powered by four AA batteries in what looks like – but isn’t – a motor drive on the base. Yashica later released Mark II and Mark III versions, both with 100mm lenses, which meant the camera-to-patient distance could be increased while retaining the 1:1 focusing. The Mark III had a built-in motor drive.