Pentax DA 70mm Limited - Possible oily residue inside lens?

Started 4 months ago | Questions thread
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Wahid Khan 1961 Forum Member • Posts: 59
Pentax DA 70mm Limited - Possible oily residue inside lens?

Hi All

Bought this lens from eBay on 1-Oct-19. After a brief inspection and testing (not thorough by any means), I packed it away waiting for spring/summer to get some real use out of it. Stored in a padded attaché case with my other 'better' lenses. Case is kept in my study which is warm and dry.

Noticed today when mounting the lens that there is what appears to be an oily residue inside the lens. I deduce this from the diffraction colours you get like an oil film on water. They disappear when I hold it to direct light and I certainly can't see any effects in the very few pictures I've taken so far.

Other than this the lens still looks mint.


1 - Has anyone else notice this sort of thing in any of their lenses?

2 - Should I be concerned?

3 - Is a relatively easy cure/fix available/recommended?

4 - Or should I just chalk this up to one of those things? Far bigger things to worry about in these troubling times.

At the moment I'm not losing any sleep over it, curious more than anything else.

Thanking you all in advance for any advice, recommendations or comments.

 Wahid Khan 1961's gear list:Wahid Khan 1961's gear list
Samsung EX2F Samsung NX10 Pentax K-5 Samsung NX1000 Samsung NX20 +29 more
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