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  1. #1
    JPD
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    RÜO Dopp-Anastigmat Iricentor

    I got this lens today, marked: RUO DOPP-ANASTIGMAT IRICENTOR 1:6,8 F=18cm OPT-WERKE RUDERSDORF-BERLIN No 2139 in an early working Compur.

    The "Vade Mecum" says it's a Dagor type, and "a really good design" according to W. Frerk.

    Most of the RÜO lenses I find on the internet have low serial numbers. I wonder how long Optische Werke Rüdersdorf were in business?

    The lens is very clean and scratch free, but has a light yellow tinge. Not much, only as an old UV-filter. What could that be? Yellowing balsam? The glass?

  2. #2
    Ole
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    There isn't much I can find out about Rüo-Optik, but there are a few leads:

    The first patent I can find under the name Rüo-Optik is dated 9/11 1920, for a projection lens. yet the same constructor (Hahn) patented the Rüo-Tele-Anastigmat 25/2 1919 under his own name. So the company seems to have been set up between those dates - other wise why would he include the "Rüo-" in the name of the earliest lens and not the later? I would guess that the company was in planning but not yet registered in February 1919.

    Hahn seems to have specialised in fast lenses. Among the Rüo products are the Calinar f:2-2.5, later f:1.5-1.8, and the Paritar f:1 (1) from 1933. I wonder what the T-stop was on a 5-element 5-cell uncoated f:1 lens?

    And yes, a light yellow tinge in a lens of that age is very likely to be yellowing of the balsam.
    -- Ole Tjugen, Luddite Elitist
    Norway

  3. #3
    JPD
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    Thanks for the information, Ole. I see that the municipality of Rüdersdorf has a web page. Maybe they can give some information about when this firm was active. Worth a try.

    I wonder if UV-light could bleach the yellowed balsam?

    I wonder what the T-stop was on a 5-element 5-cell uncoated f:1 lens?
    Interesting question. Hm, internal reflections... Some reaches the film... Could it be more than 1 stop?

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    Ole
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    No, UV light is not likely to bleach yellowed balsam - it's more likely to make it even yellower.

    If each surface reflects 5% of the light, the transmission will be 0.95^10, or about 60%. 5% is pretty optimistic, so I would guess that it loses more than a full stop.
    -- Ole Tjugen, Luddite Elitist
    Norway

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    JPD
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    But... yellowed balsam in lenses with radioactive elements is bleached with UV light? Worth a try, since I'm only shooting b/w anyway.

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    Ole
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    No, in lenses with radioactive elements it's the glass itself which turns yellow. The radioactivity creates F-centers in the glass structure, which can be removed by application of high-energy light - i.e. UV light.

    Balsam yellowing is a result of oxidation and recrystallisation of the balsam, which is a very different process.
    -- Ole Tjugen, Luddite Elitist
    Norway

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    JPD
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    Ah, thanks for clearing that up! The tinge is very faint, so it's probably best to leave it as it is. I will try the lens this spring.

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    Hello Ole, I found your words abaut RÜO by searching for information about this company.
    Rüdersdorfer Optische Werke is known in Rüdersdorf by only a handful of people. I can find two patents of lenses on the DPMA´s page - Deutsches Patent und Markenamt ( www.dpma.de  you can change the page´s language ) -. One from the 29.09.1923 and one from the 14.06.1928. Both patents are submitted by - Opt.Werke Rüdersdorf G.m.b.H. und Hugo Hahn in Rüdersdorf i. Mark
    But I´m not able to find the patents you mentioned. It would be great if you could tell me about your source. Thanks a lot for that!

  9. #9
    Ole
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    I believe I found most of the information in Hartmut Thiele's "Deutsche Photooptik von A-Z", probably also something in David's "Photographisches Praktikum".
    -- Ole Tjugen, Luddite Elitist
    Norway

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    JPD
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    IRICENTOR, another Iricentor owner?

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