Steven Tribe
16-Mar-2018, 06:01
I was checking the equivalent focal length of a newly purchased Ross Cabinet no.1 with catalogues from the late 19th century and found that this is given as 6" - which didn't agree with what I had measured it to. Must be the "back focus", so I checked a much later catalogue from 1934 from Kodak (UK) which still had the big Ross Petzvals alongside the Dallmeyer and Cooke competitors. This gives the equivalent focal length for this cabinet as 8 1/4" - which corresponds with what I had found. So don't trust the catalogue data - it may be "back focal length", even it is doesn't say so.
The description of the Ross Cabinet series says ".. diffusion can easily be obtained by unscrewing slightly the outer cell of the the lens". Checking the rear cell, I find this is not true! The complete lens cell is loosened fron the barrel. This method of introducing diffusion was that which, amongst others, Darlot had employed - and used in public discussions against the Dallmeyer Patent in the 1860's.
However, looking at the rear cell, I quickly found out that the construction was of two separately mounted lens which could be unscrewed from each other. The lenses were also exactly the same as the Dallmeyer Petzval redesign. The internal rear lens screws in towards the front cell - in exactly the same way as the later "turn the barrel" version of the Dallmeyer Patents (but a more simple design!). There is even a pair of marks to indicate the "standard position"
It could be that Ross eventually (by 1934) used a rear cell which could be adjusted from the outside. My Ross Cabinet ( 67193) is from the start of the 20th century. I would suggest that all Ross Cabinet lenses after this serial number have the Dallmeyer softness adjustment.
The description of the Ross Cabinet series says ".. diffusion can easily be obtained by unscrewing slightly the outer cell of the the lens". Checking the rear cell, I find this is not true! The complete lens cell is loosened fron the barrel. This method of introducing diffusion was that which, amongst others, Darlot had employed - and used in public discussions against the Dallmeyer Patent in the 1860's.
However, looking at the rear cell, I quickly found out that the construction was of two separately mounted lens which could be unscrewed from each other. The lenses were also exactly the same as the Dallmeyer Petzval redesign. The internal rear lens screws in towards the front cell - in exactly the same way as the later "turn the barrel" version of the Dallmeyer Patents (but a more simple design!). There is even a pair of marks to indicate the "standard position"
It could be that Ross eventually (by 1934) used a rear cell which could be adjusted from the outside. My Ross Cabinet ( 67193) is from the start of the 20th century. I would suggest that all Ross Cabinet lenses after this serial number have the Dallmeyer softness adjustment.