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seawolf66
18-Apr-2008, 10:44
I have aquired a G.Rodenstock Muchen lens # 3126 It states its a Doppel Anastigmat Lumar Serie II F:6 Foc 30cm D.P.R.a F-stop markings go from Below F:4 to F-96 also be advised that in the Vade Mercum it list a doppel Anastigmat by itself and lumar by itself but not combined?

Since it has these markings on it had an Iris in it: Which at this time it does not!

But Somebody decided to make it into a iris disk lens , So my problem is this do I go looking for a Iris for the lens or do I just start make-ing proper disk for it . if so where
will I find information on what size each hole has to be For F:11 and on up!

The very front element is fractured so any thing below F:11 may not work , I think?

the brass on the outside has turned a copper tone color , is this normal for this age brass!

I hope I have writen this in a manner you can understand: and thank you for your Time on this:

Peter K
18-Apr-2008, 11:14
Lauren,

"Doppel Anastigmat" is a kind of lens developed in the end of the 19. century. E. g. the Dagor is a double anastigmat. The name "Lumar" was used by Rodenstock also for different kind of lenses.

But your lens has to be equipped with a diaphragm, also the front piece has to dismanteled and re-cemented. At least you need a distance piece between the front and rear piece. So it's a lot of work.

The color of the brass depends of the ratio copper to zinc. So some brass is more yellow and other more red.

Peter K

Chauncey Walden
18-Apr-2008, 12:37
The simple answer on making apertures for it would be to divide 300 (the focal length) by the f/stop you want and make the hole that size. After all, that is what an f/stop is - the (f) focal length (/) divided by the diameter of the (apparent) stop. So an f/32 aperture would be 300/32 or about 9mm. This would be close enough for most government work. If you want to get more exact for some reason, you can tweak it by measuring the size of a known aperture (say 10mm) while looking through the front of the lens and use the percentage difference between actual and seen to modify your calculation.

Ole Tjugen
18-Apr-2008, 12:43
"Doppel Anastigmat" means that each half of the lens is an anastigmat; i.e. consists of two or more lenses that in combination is more or less free from astigmatism.

The vade Mecum calls the Lumar a "Gauss type", which yours is certainly not: There are no cemented pairs in a double Gauss, so decementing is impossible.

Interestingly Hartmut Thiele lists four different Lumars: Serie I, II, III and nothing. The one without series designation is a f:2.5 projection lens, the others are camera lenses. But: All are reported as 4-4; or four uncemented elements!

Also none of them (except the projection lens, which isn't likely to have had an iris aperture) had a maximum aperture larger than f:4.5. So the scale you have is probably not f-stops, but something else. I think I've listed all the "likely suspects" here somewhere, you may have to search for it. ;)

seawolf66
18-Apr-2008, 15:48
Peter K and chauncey Walden thank you both for your thoughts;
Now -Ole Tjugen : You are right it is a 4-4 two lens up front and two lenses out back
and they are not cemented But it is a serie II per the writing on the barrel , If you look at foto two you will see the indented marks and on the ring there is a small Arrow that when positioned at one of these indented marks would equal something
see new foto of the space in the barrel ; This barrel space is the same as my
Hugo Meyer & Co-Goerlitz Aristostigmat 1:4,8 for the iris to be moved by the ring
when turned and the ring on the double anastigmat has a arrow:

But thats that would like to hear from some one if they have a old iris that might fit into this lens barrel in this case it would have to be about 2-9/16inches O/D

I know I am the newbie here but i do tell you what I have ???
Thanks folks

Glenn Thoreson
18-Apr-2008, 16:43
I'm wondering if it originally had an aperture disc that you rotated to different openings. I may not be explaining it very well, but I'll bet Ole knows what I mean. It certainly appears that you have a slot in the barrel, so a set of Waterhouse stops would be easily set up. The biggest concern would be the difference in apertures if the lens is convertible. I assume it is?

seawolf66
18-Apr-2008, 19:08
glenn Thoreson: As far as I can read and see its not a convertable , But I have been wrong before: its more like Oly states 2 lenses in front and two lenses out back since I have them apart and cleaning them: thanks glenn:

Ernest Purdum
19-Apr-2008, 09:07
Check Rolyn Optics for iris diaphragms. They will probably have one close to the needed size, but it may be a little difficult to fit it into the barrel.

Ole Tjugen
19-Apr-2008, 11:12
The Lumar Serie II f:6 was made in focal lengths from 90 to 300mm. Angle of coverage was 65 degrees.

The lens was introduced in 1902, and yours must be from one of the first years since Rodenstock passed 50,000 in 1910.

What's 2 9/16" in German (metric)? ;)

Ole Tjugen
19-Apr-2008, 11:19
One more thing: With regards to old German lenses, the Vade Mecum is (sadly, and mostly) rubbish.

And another: With a 300mm lens, the difference between physical aperture and entrance pupil is ignorable. So to make a waterhouse stop for f:11 you woulld need a plate with a (300mm / 11) 27.3mm hole - or close enough to make no practical difference.

seawolf66
19-Apr-2008, 18:43
Ernest Purdum: Thanks for the lead to the royln optics company, thanks for the help:
Ernest:

seawolf66
19-Apr-2008, 18:53
Ole Tjugen: Well if # 50,000 was in 1910 then that makes mine about 1902 or 1903
and 2-9/16" equals inches and I thank you for your help here also, as you state the size of the hole is one of those [ close enough for horse shoes and hand gerandes and atomic war fare ] lol that is a play of words on being close: thanks again Ole

and I will not enter the sphire of discussion on Vade Mercum factuality:

seawolf66
19-Apr-2008, 19:20
Peter K. [The color of the brass depends of the ratio copper to zinc. So some brass is more yellow and other more red.] it looks like its lose-ing its yellow color and turning red brown , but yet the inside is bright yellow except where its painted black where
the back lens goes : thanks for the info