i need some help identifying a lens that was threaded into an older prism diagonal. This came from an old C8 kit, and was in a box labelled "R F A-ADAPTOR" . there are no markings on it anywhere. i thought the lens was a focal reducer, but after attaching the lens to my William Optic diagonal, and my Meade 2080, i am not so sure. the lens assembly has standard SCT threads and the lens assembly threaded into my William Optics diagonal perfectly. so i tested it and i had to add about 8" of back focus to focus it. i had it set with the lens, my diagonal, a porro prism then @5" focal extender. the image was not very good. am i missing something with this lens? i wouldn't think a standard 6.3 focal reducer would require that much back focus. please see the attached pictures. i am relatively new to this game and was looking for a focal reducer to try out. this came from an older C8 set up my uncle was given as a gift.