[QUOTE=ridax;1655235]One example:
https://www.largeformatphotography.i...ead.php?150772
With all due respect but that beauty ring doesn't deliver much confidence....(see for instance the misaligned numerals)
[QUOTE=ridax;1655235]One example:
https://www.largeformatphotography.i...ead.php?150772
With all due respect but that beauty ring doesn't deliver much confidence....(see for instance the misaligned numerals)
Doesn't "Series" vs. "Serie" and "7.7" instead of "7,7" plus maybe the mis-aligned numerals suggest this is one of the Burke & James "Berlin Dagors"?
David
David, I just took a look at the pictures in this thread's first post. The flange, not the lens' trim ring, is engraved "Serie III No. 1 F=150 m/m". The flange and trim ring show the same serial #, 27,575. P-H Pont's chronology puts that s/n between 1891 and 1896, closer to 1896. The largest f/# engraving I can read is 6. If Stoelze, this translates to f/7.7. What were you looking at?Originally Posted by David Lindquist
Ron, you wrote
Um, er, ah, lens' prescriptions have been recomputed for many reasons. The humble f/6.3 Tessar is an example. All the same design type. If you don't have access to the history, as David does, you wouldn't know this. With respect to Dagors, you and Ridax might want to look at the prescriptions that Eric Beltrando posted here: http://www.dioptrique.info/base/n/n_dagor.HTMIndeed, but changing the glass and aperture makes it another kind of lens IMHO; therefore they are comparable but not identical.
Yes it's suspicious. Though I've heard there was no "C.P. Goerz" on the B&J fakes.... so I'm not sure.
But B&J ones are infamous for being quite bad, and at least two of this forum members have some experience with this particular lens, and probably can tell if it works properly. But again, there might be some good lenses even among those fakes....
I'm sorry Dan, I should have quoted Ron's post just preceding mine to have been clearer. I'm referring to the Dagor shown in the link in ridax's post #17 and then quoted by Ron in post #21.
And I just looked at my Goerz Optical Co., Inc literature. It shows they mounted their 10 3/4 inch (273 mm) f/6.8 Dagor in a No. 4 Acme. The 270 mm Dagor from ridax's and Ron's link is in a No. 3 Acme, maybe this resulted in a diminution of the maximum aperture.
I'm not so knowledgeable about the B&J fakes. The late Lynn Jones seemed to think they were superior to the C.P. Goerz American Optical Co./Goerz Optical Co., Inc. versions. I say "seemed" because I sometimes found his writing a bit confusing. He did think the C.P. Goerz American Optical Company was part of the company that made sunglasses...
Also wouldn't a genuine C.P. Goerz Berlin Dagor as "new" as the one in ridax's/Ron's link appears to be have its focal length in centimeters and not millimeters? Is there a reliable source of genuine C.P. Goerz Berlin serial numbers?
Scanning ebay just now I see at least two "fishy" looking Berlin Dagors, e.g. "Series" not "Serie" and with a "." rather than a "," in the aperture designation. They are marked "C.P. Goerz" along with "Berlin." Of course there's no way of knowing if they came from B&J.
David
DAGOR = Doppel Anastigmat Goerz Optical R(?) - I forget what the R stood for. In German, of course.
My 270mm f/7.7 serial #60xxx, my 240mm f/7.7 serial #58xxx, and my 480mm f/7.7 (sorry the serial number filed off - was the lens stolen some day before I was born? But it's definitely of the same vintage) Serie III C.P. Goerz Berlin Doppel-Anastigmats are all actually f/6.8 lenses with the aperture marked up to f/7.7 only, and a stopper added inside the barrel to prevent the aperture to be fully open. THEY ARE ALL PERFECTLY IDENTICAL TO THE LATER F/6.8 DAGORS. I'VE TESTED THEM A LOT, AND I BELIEVE MY EYES.
Perhaps the most interesting thing is that my old 480mm f/7.7 is actually f/6.8 (restricted to f/7.7), too. My 360mm f/7.7 is a later Dagor-labeled one, and at f/7.7, it is really fully open. And my 360mm has smaller glass elements (relative to its focal length) then my 240mm, 270mm and 480mm Pre-Dagors and my shorter focal length f/6.8 Dagors.
And as for the Vade Mecum story - sorry I just can't believe them. It looks like they just collected all the data they could collect QUICKLY, without sorting it out - to say nothing about TESTING a single real lens - and just compiled that abstract.... They probably believed that the original DRP 74437 of 1892 contained the description of a real lens that went into actual production (anyone understanding a bit about patents knows the real inventions are kept secret, and the examples published are much inferior to the real things). And seeing the later published data on the real series III lens, they decided the design was changed.... That's just not true. (They also mention the Zschokke patents that NEVER went into an actual lens production, etc., etc.... That's not a reliable source of information.)
... Why did Goerz restrict the nominal speed to f/7.7 at first? Stopping down to f/7.7 just cuts the Dagor's positive spherical aberration to the level when it coinсides with the Gauss plane - which makes a usable image out of the ugly mess (yes I know that tastes differ, and there are people who like the.... mess) seen at f/6.8. Later, with the increased competition, the nominal speed - be it usable or not - became too important as a sales driver. And the aperture stopper was removed.
Of course I'd choose an older Pre-Dagor Double Anastigmat. Optics being exactly the same, it is the barrel that matters with this choice. The old ones are bulletproof.
I was testing my nearly new 300mm f/5.6 El-Nikkor as a taking lens on my camera a couple of years ago. I got tired and dozy and dropped the lens out of my window. It was on the ground floor but the barrel got visibly beaten, and the glass got a couple of scratches. The lens remained pretty usable but its resale value dropped about a $1,000. Another day I put my Calumet C-1 on the very edge of a table (as the rest of the table was occupied), and soon the camera started to fall down. Instinctively, I grabbed it with both hands. That wasn't the smartest move as I had my 480mm Pre-Dagor in my right hand. The lens hit the C-1 die-cast aluminum.... But the old Pre-Dagor barrel shielded the glass perfectly. In fact, I was unable to find any fresh scratches on the barrel itself. Yes I prefer the older Series III Double Anastigmats.
Last edited by ridax; 30-Aug-2022 at 00:53. Reason: typos
Another (and perhaps more important) reason not to go beyond f/7.7:
When the rays coming through the pupil edges focus at the same plane as the paraxial rays do, there is no focus shift between the wide open (f/7.7 for Dagors) lens and the lens well stopped down - say, to f/45. (Though there is still enough focus shift to worry about between f/7.7 and f/10 or f/16.)
Here is a thread where I asked about a somewhat similar Serie III Dagor to the OP's. Mine had a similar deep barrel mount and was likely from a camera with a focal plane shutter, but if there had been a focusing helicoid, it was long gone. https://www.largeformatphotography.i...e-been-mounted
Thank you Dan; I know the source(s) .(....and from my own tests - not done in a laboratory environment - it became clear to me that the later Tessar f 4.5 or f 3.5 stopped down to 6.3 don't provide the same high resolution of the first f 6.3 - which I prefer). However testing lenses is not easy, and for fair results should be done with a lot of different samples i.e. lenses since they differ (even the same types) more so the older they are.
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