One of these came with a Graflex 5x7 SLR that I just purchased. I looked it up at Cameraeccentric but honestly cannot understand the marketing jargon of the last century. It has stops from F/6 to F/45. It is marked Adon No. 2 Ser X. Serial number 88945. The front element slides back and forth in the barrel. Can some enlighten me as to what I have got?