I bought this Hanimex at an estate sale for a deceased pro photographer, and can find nothing about it. Serial number is given above. In the center of the lens is a black plastic(?) center marked Hanimex 750mm F-11. It's more than 9inches long, and the barrel is 4 inches wide. Has 4X = F22 at the base of the 4" portion. Can you tell me what it is used for, approximate value etc? Nikon mount.