I just picked up a 12" Goerz lens in an Ilex #3Acme and I am having a heck of a time identifying the exact model. Here is the exact stamping - "C. P. Goerz Am. Opt. Co. Apochromat Artar 12in F:9 No.768079". The serial numb er is repeated on the rear elements. I cannot find this f-length/aperture combo listed in any resource that I know of . All of the Apo Artar Goerz I can find are "Red Dots" - but this lens has no dot or text indicating such - The Dagors are all f/6.8 not f/9. Any of you lens gurus/historians out there have a clue about the identity of the old boy?