it is funny to read that Derogy was one of the first lens maker that went in the mass production while at the same time it is so hard to find any information even in the VM...
I'm looking to know what is the focal length of a Derogy Petzval lens #4 and #5? what is the format they were best used for? The aperture of f/4 seems to be correct.
Lens numbers changed often, then changed some more. There are no catalogs of the French makers that I know of digitized. So you have to just ask the seller the focal length and go from there. Knowing it's a #4 or #5 doesn't tell you anything, though it may have in 1868.
Garrett
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Derogy is one of the many important French makers that the authors of Lens VM didn't get much data on. They based their description on lenses that were available "for inspection" in the UK.
There are some changes in engraving style and content through the 50's and 60's. I don't recall that Derogy wrote sizes on their lenses until quite late - say the 1880's. If the numbering is huge, then it is likely the Aplanat series (see below).
It is looking like the Aplanat's number. I saw a #5 calling for 9 1/2" and another one at 10".
What were their main focal length even before starting to numbering the barrel?
I don't have a list of focal lengths for Derogy.
The "standard" for Petzvals was something like:
1 - 3. CdV sizes 4 - 6".
4 (9 - 12") and above (12" and more).
This is a very rough guide to just some makers. The early makers often had several series of Petzvals (speed) so focal length classification can be misleading.
Some differentiated CdV (1,2,3) and Cabinet (1,2,3 etc.) sizes.
A #5 9" lens sounds like a small (and fast) cabinet Petzval lens to me.
Yes, I have the same lens as well No 4 in bold engraving on the side of the lens on reverse side No 21770 Derogy Fab crown insignia Brevete Paris & Londres, slot for waterhouse stops , lens has cemented symmetrical front and rear elements with some mild balsam separation
Any ideas about this Derogy. Its listed in VadeMecum but that's about all.
Sorry, I just saw this to-day.
A puzzle! You will have to describe the front, central and rear lens cells a little. it has the bayonet system which usually means a Petzval and the position of the wheel stops suggest that too. Could it be a simplified version of the Derogy multiples, where the presence of the middle lens just changes the focal length?
Pehaps these will help...My high school french is pretty rusty
Antique & Classic Camera Blog
www.antiquecameras.net/blog.html
Probably! The middle of the second page shows a triplet. Nice to have the sizes for some of the better known lenses.
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