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Yellowing Pentax lenses

Discussion in 'AP Magazine Feedback & Suggestions' started by DaveS, Oct 28, 2017.

  1. William Parker

    William Parker Well-Known Member

    Roger,
    I think I might have gleaned this info whilst sitting in a pub chatting to a much younger friend who mentioned what a good reputation Takumars have. The radioactivity did not enter the conversation but the yellowing did. I think this is where I first heard about the exposure to sunlight theory and I subsequently must have seen it in print, perhaps the same print you read? I can state that non of my Takumars , four of them, have yellowed.

    On the same topic but different maker, somewhere on the net, perhaps eBay, I have seen s Leitz lens described as radioactive too.

    Best Wishes
     
  2. Roger Hicks

    Roger Hicks Well-Known Member

    Dear William,

    Yes, at least one, but I forget which.

    Cheers,

    R.
     
    William Parker likes this.
  3. DaveS

    DaveS Well-Known Member

    I think the UV treatment thing came up on a film-making forum I was a member of, about the time DSLRs started to be used for filming. It was in a thread about using manual lenses and which ones gave the "best" image quality. My 35mm f/2 is very sharp.
     
  4. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    A yellow lens would be good for FP4 landscapes - provided the radiation didn’t lower the film contrast by fogging. :confused:
     
  5. Roger Hicks

    Roger Hicks Well-Known Member

    Dear Andrew,

    It doesn't.

    Cheers,

    R.
     
  6. DaveS

    DaveS Well-Known Member

    The "yellowing" in my 35mm is less a clear yellow than a rather dingy yellow-brown.
     
  7. Roger Hicks

    Roger Hicks Well-Known Member

    Dear Dave,

    Yup. Typical.

    Cheers,

    R.
     
  8. Mark101

    Mark101 Well-Known Member


    Yes, the method mentioned exists on some old forums and owning some old Pentax equipment remembered mention of this too.

    The Spotmatic Group Method
    Here is the method we use on the Yahoo! Spotmatic group:

    How to Cure Yellowing in Takumar 50mmf1.4lenses.

    Remove both lens caps and wrap the uncapped lens, except the rear element,
    in aluminum foil and then set it on a windowsill that faces towards the sun.
    Prop it up with something (like a rolled-up towel) so that it tilts in order
    to get the most sunlight into it. Then go away and leave it.

    A mild case takes about a week to ten days on a windowsill in California.
    A severe one takes about a month.
    The foil serves two functions. It reflects light off the lens body and
    thus reduces heat buildup that otherwise would occur due to the black
    finish on the lens and this could affect the lubrication inside the lens.
    And by not capping the lens before wrapping it, light makes its way from
    the back of the lens and reflects back off the foil at the front of the lens,
    thus attacking the yellowing again.

    This "sunlight cure" method has been successfully employed by a number of
    members of the Spotmatic group and many 50mmf1.4lenses which were
    thought to be useless for colour photography have now been returned to
    active service with "water clear" glass.
    Some others have reported good results in about three weeks using an
    ultraviolet light source.

    The yellowing problem affects the Model II 50mm f1.4 Super-Takumars and all
    other 50mm f1.4 lens through to the K-mount series.
    The older Model I 50/1.4 Super-Takumars, the 8-element ones (which can be
    distinguished by the protruding element at the rear NOT having a
    protective metal rim), do not turn yellow because they do not have
    the radioactive element, using an additional regular optical glass element to
    get higher refraction instead. The Yellowing problem also affects the later
    f2 35mm lenses with 49mm filters.
     
    peterba and William Parker like this.
  9. William Parker

    William Parker Well-Known Member

     
  10. William Parker

    William Parker Well-Known Member

    Thanks for that info Mark, I have never owned a 1.4 so perhaps my collection is ermmmmm safe! And I can remove them from my lead lined box and stop wearing those terrible lead lined trousers

    Cheers
     
  11. William Parker

    William Parker Well-Known Member

  12. peterba

    peterba Well-Known Member

    So about 10 years and 40 years, respectively, in the UK then, Mark?!! ;)
     
  13. Mark101

    Mark101 Well-Known Member

    That quickly ? I wonder if vitamin D, ground into a paste and applied to the lens, would help?
     
    peterba likes this.
  14. peterba

    peterba Well-Known Member

    It would be cheaper than moving to California... and it would also avoid having to live under a government led by a useless idiot intent upon behaving antagonistically towards other countries. Oh, wait... :(
     
    Roger Hicks likes this.
  15. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    Cheaper still is just to pop over to Ikea. (This guy's amusing as well as having hit on a simple solution)

     
    peterba likes this.
  16. William Parker

    William Parker Well-Known Member

    We should also remember there are Super Takumars and the later Super Multi Coated (SMC) Takumars.
     
  17. peterba

    peterba Well-Known Member

    Nice one... co-incidentally, we had precisely that lamp from IKEA a few years ago. Sadly, it went belly-up after not many years. :(
     
  18. Roger Hicks

    Roger Hicks Well-Known Member

    Dear William,

    And indeed Takumars (manual) and Auto-Takumars (semi-auto: auto stop down, manual reopening). I wonder how much the actual lens designs changed?

    Cheers,

    R.
     
  19. William Parker

    William Parker Well-Known Member

    An interesting question Roger, all I do know is they are really nice lenses, having said that are there any really bad ones? By that I mean lenses in general, I suppose the answer is that some are simply better than others.

    Best Wishes
     
  20. Roger Hicks

    Roger Hicks Well-Known Member

    Dear William,

    Depends on your definition of "really bad" -- and of course sample variation after 50+ years can be significant. Some of their old wide-angles were reputedly pretty duff even when new, but I remember no details.

    Cheers,

    R.
     

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