>>4491033
Are you sure it's on the same side of the glass that you're trying to clean? Could be on the inside. It's kinda hard to tell which part you're talking about from the photo, but if it's on the rear element its probably fungus. Does it actually affect the photos? If not I wouldn't worry, I have one or two lenses with dead fungus corpses in them that I shoot with regularly as they don't come up in pictures.

>>4491040
it doesn't seem to effect pictures however I have no baseline how sharp the lens used to be.

>>4491043
It won't affect sharpness much per se, usually it would cause artefacts or flaring, or cast shadows on your sensor/film. A good way to test is to put it on a digital camera, shoot RAW in the middle of the day and just take some pictures of the sky at f/8, f/11 or f16, something like that. Maybe take some with direct light coming into the lens and see if you can see anything in the photos. If theres any dark areas or spots or anything you should see them at f/16. Otherwise it doesn't matter. Fungus won't spread once its dead, and any sunlight at all kills it pretty much instantly.

>>4491045
That's some good info, thanks m8.

>>4491047
That's all good. Oh and when I said sky, I mean just blue sky with no clouds. This is because it's really bright and really uniform and makes any inconsistencies stand out.

look up the lens elements structure , I am guessing this is most likely degraded cement that keeps duplet elements glued together but due to age its decomposing and so both element are slowly separatingand theres this inner crust, if you feel adventorus disassemble it just this back section and separate both elements carefully then clean up the cement with nail paint remover
https://www.truelens.co.uk/separating-and-re-cementing-elements

Hard to tell if it is hazing or balsam separation.

>>4491033
https://www.youtube.com/watch?v=lc1C2dKx7gc