Can you diagnose this patchy look of the lens?

[erian]

I am considering to buy a Rodenstock Eurygon 300mm 4.5 but on closer look it appears that the front glass is a bit patchy and I could not think what to make out of it. What could it be?


Images used with authors permission.

I do not want to suggest something to avoid biasing your opinion.

[Bob Salomon]

Fungus

[erian]

Fungus

Should the fungus look more like a spiderwebs or this is an early stage of it? Or this is the result after cleaning?

[Dan Fromm]

It is filthy, may or may not clean up.

[tgtaylor]

Although I can't make-out the full extent of the glass from your photos, I would suggest that you go the a drug store and purchase a small bottle of 91% isopropyl alcohol (100% would be better but 91% is what the stores carry), and clean the lens using good lens wipes like the old Kodak wipes which don't scratch the lens and a micro cloth. It may take several applications but a couple of weeks back I cleaned a MC Hoya filter with 91% that looked far worse than your lens. Several applications using a lens cleaner sold in the camera stores didn't do a thing and actually made things worse by leaving behind a residue! The alcohol worked and is cheap - like maybe $2 or so for a 16oz bottle whereas the junk sold in the camera stores cost several dollars an ounce and doesn't work.

Thomas

[Mark Sawyer]

Could be damage to the AR coating, which won't clean off but won't affect the image much, if at all.

[Bernard_L]

Could be damage to the AR coating, which won't clean off but won't affect the image much, if at all.

+1
Your images show reflection. In actual use the lens operates in transmission. Say the AR coating is degraded and its reflection coefficient fluctuates between 0.5% and 1%; twice as much; a dramatic change. At the same time the transmission varies between 99% and 99.5%. Who cares? Plus, these patches are totally out of focus.

[EdSawyer]

Agreed, looks like a coating issue. Should probably not affect images at all. Does not look like fungus.

[Doremus Scudder]

Looks like a coating problem to me too. Such damage can cause unwanted flare and scattering. I've got a WF Ektar with a similar issue and need to shield the damaged area to avoid flare. If you do get the lens, use a good compendium or hood with it.

Doremus

[erian]

Thank you everyone for the valuable input. I too thought that it might be a coating issue but I have not seen one and were therefore not very confident about it.

What can cause such issues? Could it be still caused by a fungus?

If it is some explainable coating issue then I will be not very worried.