Recently I aquired a big Ross Portrait lens. On the one side of the rack&pinion barrel there is a sign "Ross London 13766" and on the other side: "No. 3 A.P."
The disassembling showed that it's a petzval lens although it has a bit different look than other petzval lenses I met. Its front lens element is significantly smaller that the back lens.
Front lens - 83 cm in dia.
Back lens - 10 cm in dia.
Focal distance - 36 cm (approx 14 in) measuring from the waterhouse stop.
According to its serial number, the lens was made early in 1870es. Vade Mecum says that at that time Ross made 4 types of petzval lenses (different in size): No.1, No.2, No.3 and No.3A. The engraving on my lens showed that my lens is probably the last one (and the last letter "P" in its engraving may mean "Portrait"). But Vade Mecum says that No.3A should be 16 in in focus, but my lens is only about 14 in.
So there are only questions:
- Maybe it's fake Ross lenses?
- Are there any petzval lenses with the smaller front lens?
- If there are, what was the reason in such difference in size and why most of the petzvals contain lenses equal in size?
- If it's definitely Ross, why there are about 2 in difference between real and advertised focal distances?
Your answers, opinions and information will be highly appreciated!