12-40 examination - weird "film" on internal glass?

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dotdose New Member • Posts: 6
12-40 examination - weird "film" on internal glass?

Hi all,

Was cleaning my lenses today and decided to peer down the barrel of the 12-40 with a direct LED light source. Really weird occurrence - when you have the light source and your eye lined up such that you can only see green bouncing back, there's this weird splotch on the optics, in a "C" shape (think donut with bite taken out).

It's transparent, and has the visual consistency of water being sandwiched between two pieces of glass.

Any thoughts on what it could be? Don't think it looks like mold or fungus, it's more of a light film of some substance (or maybe coating of some sort wearing through?)

Thanks.

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