I recently picked up an odd F4 that I know nothing about. It has a different grip, there are electronics inside, instead of batteries, and has the addition on the back. It has a hole in the pressure plate, so I assume the film can be marked in some way. The back is wired into the electronics. Since there is no place for batteries, I assume the camera runs on external power. The plug on the front is different than a usual MB-21 grip.
First I thought the camera is modified with a punch mechanism, to mark image position indepent of perforation holes position.
Such is typically done for slides making.
There should be a corresponding hole at the lower film guide.
But there is no manual actuator on the back for that punch, and that longitudinal casing does not fit my idea either.
Is there a lamp or a sensor behind that pressure plate??
That modification might correspond to the electronics in the battery chamber.
In any case there is a one-channel electrical connection between back and body (a tensioned pin under the presure plate).
There is a photocell/lens device behind the hole mounted on the back. It corresponds to the inter-frame spacing. There is nothing mechanical here, and the camera body itself appears unmodified in any way. It appears that this exposes something onto the film.
Looks like some kind of data back.
If so,we know the output of the electronics. Is there some input too? Are the electronics wired to the non-standard connector at the front of the battery pack?
Possibly. There are 3 buttons on the back that indicate a mode selection and way to advance. There is a non-Nikon plug too, that may attach to some sort of external interface. It must provide external power, as there is no place for batteries.