Strange Ross Petzval lens

[evgenys]

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!

[CCHarrison]

You do seem to have a Ross 3A "P" ortrait lens.

Perhaps this ad will help you regarding assembly.

Dan

[evgenys]

You do seem to have a Ross 3A "P" ortrait lens.
Perhaps this ad will help you regarding assembly.
Dan

I already have found this ad somewhere in the Internet. But the scheme of the lens structure in this ad shows that the front and the back lens elements are equal in size. Mine ones have difference of 1,7 cm. That's why I've started to ask questions.

If you are just measuring the length from a focussed "infinity" image to the objective - you have remembered to measure to the Waterhouse slot position?
Absolutely genuine and nice to see one instead of all the Dallmeyer Petzvals!

Yes, I measured the distance from the infinity to the waterhouse slot. It is 36 cm +-1mm. That is 14,17 inches and is significantly (I suppose) different from the advertised focal length of No.3A lens.

[Jim Galli]

Yes, I agree. It is odd. So much history is lost. Who knows what happens after so much time. Did the guy walk into Ross and say my Studio is short, can you make it a 360mm instead of 405? And this is what they gave him. Hard to say. Enjoy it.

[Tom Sobota]

I have a Ross Cabinet n.1 somewhat later than yours (s.n. 32117, between 1875 and 1880). Front and back elements are of similar diameter, and the lens is generally as described in the catalog page sent by Dan. Also, the text ("32117 Ross London") is perpendicular to the longer dimension, not alongside it as in your lens. But then there is a 10 years difference between both lenses, so who knows.

Tom

[Louis Pacilla]

Check this out
http://books.google.com/books?id=1mc...lenses&f=false

I don't know if this helps but in 1864 the 3A was 12" FL . I don't know if this is measured from the back or stop. But at least it shows how FL/model # changed with over time with most manufacturers including Voigtlander & Dallmeyer.

[evgenys]

Thank you all for your replies!

Check this out
http://books.google.com/books?id=1mc...lenses&f=false

I don't know if this helps but in 1864 the 3A was 12" FL . I don't know if this is measured from the back or stop. But at least it shows how FL/model # changed with over time with most manufacturers including Voigtlander & Dallmeyer.

The dimensions of the lens elements of Ross No.3A in this book are the same as of my Ross lens.
But the difference of the focal length is still strange. I'll try to measure the focal length of my lens using more scientific methods an then we'll see the truth.

But there is another question arised: how to measure the maximum aperture of such lens with different lens elements? As usual, dividing the focal distance on the measured diameter of the front pupil?

[Steven Tribe]

If you are just measuring the length from a focussed "infinity" image to the objective - you have remembered to measure to the Waterhouse slot position?
Absolutely genuine and nice to see one instead of all the Dallmeyer Petzvals!

[goamules]

Hi evgeny, Good to see you're getting ready to use that lens. I researched on the Internet also (good find Louis) but didn't discover any reason why the front and back elements are such different sizes. Like we know, most of the time they are very similar sizes, front and rear. I have seen a few where the rear is slightly smaller. But I would say if the lens creates a nice image, use it and enjoy. It's certainly not a fake, the engraving looks correct. Perhaps it was made as a custom order like Jim says, for some forgotten reason or scientific use (like an astronomical telescope).

[vitality]

I've go a question about Ross lens.
Is Ross lens marked "Cabinet No. 3" the same thing as Ross "Portrait No. 3"? Checked info, for me looks the same, just different markings? (may be with time they changed markings) Or there is difference?