Canon F-A

Canon F-A with motor-drive MZ images by John-Henry Collinson (Image rights)

The Canon F-A is a 35mm SLR camera for ophthalmic examination ('Fundus photography': photography of the back of the eye, including the retina and macula and associated blood vessels.), produced in small numbers by Canon in about 1980. It appears to be based on one of the mainstream A-series cameras (perhaps the AE-1: the controls on the left of the lens-mount are the same), and has a normal FD bayonet flange, but also several strange features:

• The image frame in the film chamber is not rectangular; it has curved ends, perhaps suggesting use with a lens whose image circle does not cover the full frame. The mask also has a second small frame in its bottom-left corner; this allows limited data imprinting, of a small piece of text (e.g. the patient's name) or an exposure serial number, or the duration of exposure.
• The mirror in the camera is unusually large. A forum post at phototrio.com states that the mirror fouls a normal FD lens when released, and that the camera must be used with bellows or an extension tube. In fact, the manual for the fundus camera warns that the reflex mirror will break if released with an FD lens in place.
• Another post in the same forum thread states that the viewfinder image is upside-down and reversed; that is, there is no pentaprism in the VF.
• The camera has a large, circular eyepiece, with dioptric correction between +2 and -4.

A motor-drive, Motor Drive MZ, was made for the camera. This has six electrical contacts in a row on the front. These allow the camera to be controlled via the large ophthalmic instrument CF60-ZA of which it forms only the recording part.

The lens is fitted to the instrument, not directly to the camera. In use, the patient is positioned for photography using a chin-rest, and the lens is approximately 45mm from the surface of their eye. The instrument allows zooming between 20- and 60-degree views. It can be used for simple colour photography of the rear of the eye, after applying mydriatic eye-drops (which dilate the pupil of the eye; later fundus cameras do not require these). It can also be used to photograph the eye after staining with fluorescein. This requires special filters, inserted in a slot in the instrument. Another slot allows the insertion of cards, hand- or type-written with text to be imprinted on the film. The eye may be continuously illuminated with a halogen lamp, or by flash.