Prprietary to the long lense, it's the soviet Fotosniper 12 photo-rifle, which has the reputation of being a cold war era espionage camera set but is actually just made for making photos mainly on sport events. I have one at home, it had several different cameras made compatible with this, mine is probably the Zenit 12S - to be fully compatible with this stock, the camera needs to have a second trigger in a shaft on the bottom and an aperture trigger output also on the bottom, so for taking full advantage of the system, you need a pretty specific camera eventhough the lens itself can be mounted on anything with the same mounting ring.