Hi everyone. I've broken down and cleaned up a few petzvals. I've re-laquered, re-cemented and hammered out a few dings. But, I am baffled by the Dallmeyer portrait petzval. In the images below I have a front element of a 3B. Can anyone suitably experienced enlighten me on where and how this comes apart.
Many thanks in advance,
Leo
And here's a couple of images of the rear...
This text below was about to be initial reply, but doesn't apply to your 3B. I think that it is a quite late model where the lathe closure system had been given up. I haven't worked on this type but think there is the pressure insert end ring which I mentioned in the first text. I think the internal end ring goes into the main at the first "indentation" from the top in your first photo. This indentation doesn't look it was made in a lathe. Something like a blunt kitchen knife- sturdy and with a slight wedge effect - will tell you if wants to come apart. I don't think there is a thread there as Dallmeyer would have provided some kind of surface for friction.
There is no chance of damage to your precious achromat - but watch your hands!
Bad news, I'm very sorry!
Just like the two rear cell lenses, this front cell uses the quick lathe method of turning over the thin edge of the brass ring over the achromat! I have no idea why Dallmeyer refused to use the thread fixing ring used by (especialy) French makers.
Perhaps because it ensured that work on the front achromat (Recementing after 50 years?) would be done by a professional workshop, rather than the owner? Or, perhaps, because they knew that distortion of the lens fixing thread makes removal well nigh impossible.
I am sure there are various detailed mounting differences during the decades of production. It is very difficult to find out if the brass cell is one piece, or whether there is a type of end ring which has been inserted between the lens and the main cell brass turning. Certainly, Suter used this system and it is impossible to detect from observation!
Bending the thin brass back by hand can be done. It requires soft tools and gradual progression around the circumference. Once you have opened up a gap of around 0.5mm, it goes quite quickly.
There is a high risk of the brass edge cracking, especialy in cases where this has been done a few times before, so don't expect a perfect result. Pushing the brass edge back in place after a service is just as likely to cause some flaking of the edge.
Last edited by Steven Tribe; 3-Apr-2018 at 02:30. Reason: safety warning!
Thanks Steven. It's years I've been coming to this site and I've come to know your name very well. I'm very grateful you could point me in the right direction!
Leo
I would guess that someone like Grimes' establishment would have seen this version sometime. Is it the 20th century "turn the barrel" version and the serial number is ...? It would help others who need a front lens service.
This is a rack and pinion lens but the brass is thicker than most I've seen. I don't have a serial number, unfortunately.
I might have seen this lens before - if it has the brass sleeve without serial number! There was a 3b for sale by a very reputable seller in Germany some time ago. Everything matched with a 3B - it was just missing the right engraving.
I can't find the correspndence, but I suggested it might have been made on the continent by a major maker using another 3B as a "bench mark" (Liesegang is known to have done this quite a lot!) or a "loss" from Dallmeyer before it reached the engraving workshop.
"Benchmark"!!!! What a beautiful euphemism!
All serious makers must have bought-in some of their competitors' new products and taken them apart and measured up refractive indices and surface diameters. We must remember that patent protection was restricted to quite a limited period in the 19th century!
I want to clear some air.
I bought the 'Dallmeyer 3B half' in question on a whim from Steven Tribe some years ago on this forum's FS thread.
I recently sold it after giving up hope of finding the other 1/2, again right here on this forum.
No one is complaining about anything yet.
We all know the rules of the FS thread. Good rules.
I am a complete novice about anything Petzval or Dallmeyer and long ago decided to not lust for one. I bought Kodak and Cooke.
I now regret I faltered and bought a piece of history.
End of my story.
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