Guess the defect

[Pancolart]

It seems to me this is not a fungus or coating damage but rather crystal entity like found in prisms:

Otherwise it is tempting Ebay Item: Click here to see on Ebay.de
but what do you think?

[woodrim]

Oil spot.

[calvin83]

I have a Schacht lens with similar problem and it cannot be cleaned.

[kuuan]

not coating problem, are you sure? I would have thought that is is..

[calvin83]

May be oil or coating etching. Hard to tell because they look similar.

[iangreenhalgh1]

79eu for that? Oh dear...

[guardian]

[Pancolart]

After reading your replies and rethinking i could go for oil spot too. Especially with those drop like spots and seller's description.
Do you agree with Ian on the price being too high? It is uncommon lens and if glass is good...

[calvin83]

Pretty rare but definite not worth for 79EUR. They can had for much less if you are patient.

[woodrim]

[luisalegria]

I guess coating damage also, cause unknown but could easily be reaction to oil or other solvents as said.
I have seen several varieties of this sort of coating problem on Schacht, Steinheil, Piesker and other German lenses of that period.
As for cleaning - if it does not cause a problem in results I would leave it alone. I think it should work just fine.

I have cleaned off bad coating problems (cases where surfaces were totally eaten/ruined by fungus for instance) with aluminum polish. That will remove all the remaining coating along with the other problems, hopefully. Doesn't always work but if it is just on the coating it might. The effect of removing the coatimng from just one surface on a simple lens like this should be inconsequential.

[woodrim]

[luisalegria]

Yes -
http://www.mothers.com/02_products/05100-05101.html

Usually polished by hand with tissue, but also sometimes with dremel polishing wheel.

Sounds weird, sound like it does bad things to the lens form, etc.

Still, it has worked sometimes with no bad effects I can see.

[woodrim]

Yikes. I use Mothers' on a daily basis on aluminum. Naturally, it is an abrasive. For finer work I use Simichrome. I never considered it for lens glass. I have to believe it would leave fine scratches that would be visible with a very bright light. Cerium is a very fine polishing powder that gets mixed with lubricant (water) for polishing glass and optics.

[luisalegria]

I check for these scratches, etc. with some care, and I see no effects like that.

My main worry is of changing the form too much and thus affecting resolution, etc.
But I haven't seen that sort of problem either, or at least before and after shots only show improvement.

[woodrim]

I'm surprised there aren't scratches, but I would be more surprised if it actually altered the optical shape; that would require an abrasive that would remove glass and you would have known if you did that. I suspect cerium applied with some sort of power polishing would do the job too. But as you said, the coating would be destroyed.