This runs on four rugged racks fitted to the camera standard that mounts like a lens into the camera body. The lens fits into the front standard, and is driven along the focusing stage with a rack and pinion movement that can lock and hold any position with a clamp screw. Extension from 67mm to 204mm can be set using the scale on the side of the rack. The stage itself has a 1/4 inch tripod socket.
Note: I have just one brand new unit left. These had originally a list price of nearly $1500 which I have marked down for this last unit which is NOS (new old stock).