[Imerino]

Hi all,

First of all sorry if this forum is not the correct one for this post, I didn't see a more appropriate place to post my question.

Recently I bought a Pentax M 50mm 1.7 on ebay. The lens was supposed to be in good condition, no fungus etc. At the beginning I didn't see anything wrong except a little bit of dust, normal for a lens of 30 years... but after a more deep inspection I detected a small sign in the 2nd rear element.

As it was small and is in the corner of the lens it was difficult to identify what it was so I decided to dismount the element and here is the picture I have taken.

What do you think, is fungus or just a flaw on the coatings? I have seen fungus before in other lenses and it was obvious but in this case is so small that I am not sure...

Than you!

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Since you have it apart why not just try cleaning it?

[Reed]

It does not look like fungus, more like glass inner adhesive gone bad or some glass fault(seen some similar marks on soviet lenses, but never on made in japan lens)

[Imerino]

Thanks for your response. My main concern is not if the image quality would be affected, I am pretty sure that will be not, especially in an APS-C sensor. My main worry is that I don’t want to spread the fungus in my other lenses or the camera.
If is not fungus I will use the lens without trying to clean it.

[gofour3]

+1 for lens separation.

Looks like the front elements in my M75-150/4 zoom and no it does not affect image quality.

Phil.