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Spotting on lens element of EF 200mm f/1.8

Started Mar 25, 2021 | Discussions thread
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mfurseman New Member • Posts: 6
Spotting on lens element of EF 200mm f/1.8

I recently purchased a EF 200/1.8 for a good price knowing that the lens contained what appears to be fungus with the intention of disassembling and cleaning the lens myself. I have now removed the front group and disassembled it but am unsure what the spotting on the lens is. Pictured below is the rear element from the front barrel assembly, CY1-2609:

Rear element from front barrel assembly of Canon EF 200mm f/1.8 (CY-1-2609) showing spotting.

From tilting the lens and looking through it looks (although it's hard to tell) like the spotting is on rear surface. I have attempted to clean it with acetone although there was no change. I'm unsure if these marks are fungus, concrete separation, or etching caused by previously cleaned fungus; the lens does appear to have been opened up before, which isn't surprising given it was manufactured in 1989.

The element from another angle:

Rear element from front barrel assembly of Canon EF 200mm f/1.8 (CY-1-2609), tilted view, showing spotting.

P.S. Mods: there does not seem to be a product tag for the EF200/1.8!

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