cyberjunkie
24-Jun-2012, 10:03
Some time ago i purchased a lot of old brass lenses, from Germany.
Today i was cleaning the last one, a nice projection lens made by Riechert, Wien, and i discovered that the lens had been reassembled the wrong way.
It is a 200mm Solar, with no diaphragm, and with rack and pinion focusing. It is attached to a wooden board, probably from a magic lantern.
Each cell is made by a positive meniscus, and a negative doublet, with blackened rim.
The lens is not symmetrical, one of the cells has a distancing ring.
As i found it, the lens had the ring placed in the wrong cell, and the two groups in the other cell were reversed.
I think i have corrected the most evident problems, but i am at loss with "fine tuning".
Practically speaking, i don't know which of the two cells goes at the front (with ring, or ringless?), and how to mount the two doublets (thinner element towards the inside or the outside?).
It is the first projection lens which is neither a petzval nor a triplet, hence i can't take any advantage from personal experience.
The Vademecum is of no help either (there is an f/6.8 dialyte, which is NOT my lens), and i couldn't find find any practical informations online. Just an identical lens on sale on Ebay, for a high price (although i must admit i don't have the slightest idea of how much it could be worth).
My only hope is to find a nice soul who owns the same lens, and who's willing to take a peek at its own example.
I hope that in the near future we will see a much needed documentation site about projection lenses (like, for example, what has been done by Dr. Klaus Schmitt for macros).
P.S.
During my first examination, i saw 5 reflections for each cell, thus i took for granted that the internal negative element was in fact a doublet.
I am not so sure anymore.
The rim of the element is blackened, there is an imperfection that looks like a seam between two cemented glasses. Again, not so sure about it. I have to reopen the lens and look better.
It could be a very fast dialyte. Not an f/6.8, as the Vademecum suggest, more an f/4 (that's the ratio between FL and diameter of light path).
Today i was cleaning the last one, a nice projection lens made by Riechert, Wien, and i discovered that the lens had been reassembled the wrong way.
It is a 200mm Solar, with no diaphragm, and with rack and pinion focusing. It is attached to a wooden board, probably from a magic lantern.
Each cell is made by a positive meniscus, and a negative doublet, with blackened rim.
The lens is not symmetrical, one of the cells has a distancing ring.
As i found it, the lens had the ring placed in the wrong cell, and the two groups in the other cell were reversed.
I think i have corrected the most evident problems, but i am at loss with "fine tuning".
Practically speaking, i don't know which of the two cells goes at the front (with ring, or ringless?), and how to mount the two doublets (thinner element towards the inside or the outside?).
It is the first projection lens which is neither a petzval nor a triplet, hence i can't take any advantage from personal experience.
The Vademecum is of no help either (there is an f/6.8 dialyte, which is NOT my lens), and i couldn't find find any practical informations online. Just an identical lens on sale on Ebay, for a high price (although i must admit i don't have the slightest idea of how much it could be worth).
My only hope is to find a nice soul who owns the same lens, and who's willing to take a peek at its own example.
I hope that in the near future we will see a much needed documentation site about projection lenses (like, for example, what has been done by Dr. Klaus Schmitt for macros).
P.S.
During my first examination, i saw 5 reflections for each cell, thus i took for granted that the internal negative element was in fact a doublet.
I am not so sure anymore.
The rim of the element is blackened, there is an imperfection that looks like a seam between two cemented glasses. Again, not so sure about it. I have to reopen the lens and look better.
It could be a very fast dialyte. Not an f/6.8, as the Vademecum suggest, more an f/4 (that's the ratio between FL and diameter of light path).