Rodenstock Rodagon 50mm 2.8 Stiff aperture ring

Discussion in 'Enlarging' started by Svenedin, Jul 15, 2016.

  1. Svenedin

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    I have a Rodenstock Rodagon 50mm f2.8 that I acquired second hand a while ago. Unfortunately the aperture ring does not move smoothly. It is very stiff, so stiff in fact that the lens tends to come unscrewed from the lens board when changing aperture. It is possible to disable the click via a slider but even then the aperture ring is stiff but much less so than with the click enabled.

    Does anyone know how I can access the click?

    It seems that the problem is with the aperture ring mechanism rather than the aperture itself. It may be gummed up with old grease and dirt. I don't want to disassemble the lens too far as I will probably ruin it but at the moment it is unusable and probably not worth professional repair so I suppose I don't have a lot to lose. It looks like the plastic parts, including the aperture ring, form a collar around the metal cylindrical core that contains the lenses. There is a plastic locking piece let into the top surface that might come out with a drift and release the plastic collar without any need to remove lens elements. I am reluctant to investigate further without knowing what I am doing.

    Incidentally there are some odd markings on the lens "AR 400-820 nM" which seems to refer to light wavelength.
     

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    Last edited: Jul 15, 2016
  2. randyB

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    I have 2 of the Rodagon 50/2.8's. You have to be very careful taking them apart. On mine, the front group holds the aperture ring and blades in position. I made the mistake of wiggling the aperture ring after removing the front group and all the blades fell out, it was a pain getting them back in correctly. Perhaps your front group is just screwed a little too tight.
     
  3. OP
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    Svenedin

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    @randyB Thanks You. Do your lenses look like the same design as mine? Maybe I will slightly loosen the front group retaining ring and see if that makes any difference.

    Stephen
     
  4. randyB

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    Mine appears to be the same design as yours. What I loosened was the front part with the writing on it.
     
  5. Nicholas Lindan

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    "AR" usually stands for "Anti-Reflection" - so I'd guess the AR coatings are for 400-820 nM, which isn't needed for an enlarger lens. 400-580nM would be plenty, paper isn't sensitive to yellow->(very) near IR.
     
  6. BMbikerider

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    The Rodagon can form light corrosion inside on the track where the ball for the click-stop is located. I sent mine to an optical engineer who cleaned it out and applied dry lubrication.(Graphite) (so it doesn't spread) Grease can migrate if the lens gets hot, which enlarging lenses can do, so now it is as good as new.
     
  7. OP
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    Svenedin

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    @BMbikerider Much obliged. I still have the lens and it now sounds like it can be fixed. Thank you.
     
  8. BMbikerider

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    Svenedin have just noticed that you are from UK. Where I sent my lens was to:-

    The Camera Repair Workshop in Bletchley near Milton Keynes. Tel 01908 378088. His turn around was about 5 working days. It was returned like new and his charge included carriage. It is best to give him a call, he does sometimes get very busy.,
     
  9. OP
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    Svenedin

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    Super. Thank you. I do have a contact via a local camera shop but he takes untold months to do the work (but a very good job when it's done).
     
  10. chip j

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    Use clock oil around the rims of the aperture scale. I loosened up a few rings w/that, incl. one that would hardly turn! (works like new now).
     
  11. BMbikerider

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    Some may be happy to let a small amount of oil enter the inside of a lens, but that is beyond the pale. There is no control where it may end up and you could be faced with the job of cleaning it as well as proper lubrication. Introduction of a thin oil is a suggestion which I or many others would not care to follow. If there are any foreign deposits causing the lens to become stiff, introducing a lubricant without knowing where it was going to go may cause any foreign matter to migrate into other mechanisms. Not really what anyone would want.
     
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