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Blemish inside 16mm 3.5 rear element

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It was sold as ‘junk’, but it appeared to be in mint condition - until I noticed a crescent shaped blemish on the inside of the rear element.

Any ideas what it is?

I think I will need to pluck up the courage to follow Richard Haw’s maintenance guide …

Roland Vink:
Hard to be sure. There are two sets of cemented elements in the rear, so it could be separation. If so, it will be difficult if not impossible to repair. Does the blemish change colour or disappear when viewed from different angles?

No, it keeps the same size and shape, and color :(

Easy enough to get into, but I am finding it impossible to separate the two sets of cemented elements. The inner one refuses to budge,

It looks like separation.  I have one lookin nearly the same but in some worse condition. It's same model with same problem. Mine was bought for parts- AI ring. My technitian from SPb, Russia, former engineer from USSR military optical fabric, told me that he could separate and then clue back my but there is no need for that (because it's for parts) He successfully did that operation many times on old Leitz lenses and early Canon EF lenses. But he using the same clue(balsam) for all lenses because of balsam availability. So after repair lens may be not as it was originally. Probably in your location there is such trained technitian.


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