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Old Sigma Lens problem

Discussion in 'Lens Matters' started by Eye Robot, Jul 23, 2012.

  1. Eye Robot

    Eye Robot Well-Known Member

    Sigma question in two parts, sorry:

    Sometime in the early - mid 1990s I bought a Sigma 400mm Apo for use on a Canon EOS 10 a 35mm film camera (probably about the start of the EOS name). It's been in a cupboard for a long time.

    I dug it out yesterday and was alarmed to find that the coating on parts of the lens body was sticky and coming off like tar or Marmite. Apparently it is the zen coating and problem is known about. Exactly as in the image in this post I found when searching for the problem:

    Question 1: Does anyone know the best way to deal with this?
    I could try removing it with Meths, White Spirit or Nail varnish remover, but I thought I would ask advice.

    Question 2: If I rescued the lens from the sticky stuff is there any way of using this lens on (say) a possible future EOS 650D? Would this also apply to the two Canon kit zooms I also have?
  2. Mr Mischief

    Mr Mischief Well-Known Member

    Funny I just bought the 400mm f5.6 version of this lens.. as it was cheap...;)

    it works on my 7D but you need to use it on AV and have the apature on 5.6..
    if you change it the camera reads error.. and you have to switch the camera off and on..

    but for birds etc.. its fine.. as its a cheap lens...

    sorry no idea about stickyness...

  3. frank1

    frank1 Well-Known Member

    Sorry can't help you at all just to say. I'll have to look at all my Sigmas now. I suppose best to remain zen about ok I'll get my coat. Have you emailed Sigma.
  4. nimbus

    nimbus Well-Known Member

    The coating problem is known, as is the chipping issue described by Mr Mischief. Essentially older Sigma lenses have chips that are not compatible with later EOS cameras, it was, and may still be, possible to have them re-chipped by Sigma. I had a 300mm f4 APO updated.

    With regard to the Canon kit lenses, there should be no compatability issues between these and any EOS body. The problem with Sigmas was down to them reverse engineering their chips.
  5. Eye Robot

    Eye Robot Well-Known Member

    Thanks for replies. I haven't emailed Sigma but there isn't anything on stickiness on their website under FAQs or troubleshooting.
    The only refs are on other forums where someone suggested 90% Alcohol. I was wondering if someone here had tried to remove the coating successfully and what they used. I'll give it a day or two to see if anyone has, otherwise I'll try meths and I'll post back the results for posterity.
  6. El_Sid

    El_Sid Well-Known Member

    I suspect this problem is very similar to the one often seen with the light seals around film camera backs and the underside of the focus screen where the mirror rests - the rubber (a butyl type I believe) simply breaks down and goes sticky. A similar issue can also affect the rubber buffers in the shutter mechanism of old EOS cameras (I has 600 that suffered this). The recommended cleaning fluids were either meths or lighter fuel - if you use either do it outside or in a very well ventilated room as you are lilely to need quite a lot to sort an entire lens...

    A possible alternative may be to use either talc or finely divided chalk (the stuff that used to come in bike tyre repair kits) to dry up the coating. The potential downside here is that there is a risk of dust getting into the lens and you'd probably need to repeat the treatment as the degradation of the rubber continues...
  7. Eye Robot

    Eye Robot Well-Known Member

    I spoke to someone at Sigma this morning and was told that this lens cannot be re-chipped.

    As regards sticky "tar". I've been trying Meths and it works, but it is going to take several sessions to remove completely. The one plus to this is the nastiest, stickiest stuff is also the easiest to remove.
  8. GeoffR

    GeoffR Well-Known Member

    Unless the lens body is metal, don't use nail varnish remover, it will dissolve many plastics and I don't think that is what you are trying to do.
  9. eagerbeaver

    eagerbeaver Well-Known Member

    Why oh why do camera makers use this foam rubber? you cannot blame one maker, they all do it. I hve several medium format cameras and they all suffered from this. You have to wash it away with meths then use felt to replace it .

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