Fungus on eyepiece lens

[RobertI]

I’ve just cleaned some eyepieces which were used during an outreach session last night (people must have really greasy eyelashes!). Whilst checking my other eyepieces in the case I noticed my 38mm Panaview had three or four spots of fungus on the outer edge. After cleaning with Baader Wonder Fluid, the fungus is gone, but there are areas which look like water marks which cannot be removed - I am assuming this is permanent damage to the coating? Interestingly the ‘watermarks’ appear more widespread than the original fungus so I’m wondering if some of the fungus was not visible?

I’m not bothered, I’m pretty sure there will be no impact to the views and it’s a cheap eyepiece anyway, but just wondering what people think. 

PS: I don’t normally remove lenses, but the fungus was creeping under the retaining ring. 

[Elp]

If it's fungus you can leave it out in sunlight (not indoors as windows filter some UV out), this will kill it off.

Obviously if it's part of an assembly (eg camera lenses) thought has to be put into this method as you don't want to melt parts or affect lubricants etc. And more obvious do not allow any through light rays to reach a fine focal point.

Edited April 8 by Elp

[Don Pensack]

5 hours ago, RobertI said:

I’ve just cleaned some eyepieces which were used during an outreach session last night (people must have really greasy eyelashes!). Whilst checking my other eyepieces in the case I noticed my 38mm Panaview had three or four spots of fungus on the outer edge. After cleaning with Baader Wonder Fluid, the fungus is gone, but there are areas which look like water marks which cannot be removed - I am assuming this is permanent damage to the coating? Interestingly the ‘watermarks’ appear more widespread than the original fungus so I’m wondering if some of the fungus was not visible?

I’m not bothered, I’m pretty sure there will be no impact to the views and it’s a cheap eyepiece anyway, but just wondering what people think. 

PS: I don’t normally remove lenses, but the fungus was creeping under the retaining ring. 

It could be water spots from the fluid, and/or, perhaps, the cleaner isn't strong enough.

To find out, try pure acetone on one of the spots to see if it comes off.

If it doesn't, it is likely to be coating damage.

[Carbon Brush]

Difficult from a photo but my thinking is chemical residue or coating damage.
Good call from @Don Pensack on acetone. You might also try isopropanol.

My experience of coating damage has been worn areas resulting from someone being over enthusiastic, many times, with a cleaning cloth on binoculars.
Another (actually two people) was spectacle lenses losing coating after repeated cleaning using isopropanol. An odd clean won't do harm.
The specs lens developed cracks in the coating and got to the point where a finger nail could flake off areas.
For reference the specs came from 'should have gone to'.

Your photo doesn't look like either of the above. It loks to be well defined round areas. So I'm hoping a bit of the right chemical will do the trick.

Let us know how it goes.

[dweller25]

Good luck Rob 👍

[Alan White]

How did this work out Rob?