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View Full Version : Can you diagnose this patchy look of the lens?



erian
18-Nov-2019, 19:03
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?

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Images used with authors permission.

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

Bob Salomon
18-Nov-2019, 19:15
Fungus

erian
18-Nov-2019, 19:17
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
18-Nov-2019, 20:16
It is filthy, may or may not clean up.

tgtaylor
18-Nov-2019, 20:36
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
18-Nov-2019, 23:38
Could be damage to the AR coating, which won't clean off but won't affect the image much, if at all.

Bernard_L
18-Nov-2019, 23:59
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
19-Nov-2019, 08:49
Agreed, looks like a coating issue. Should probably not affect images at all. Does not look like fungus.

Doremus Scudder
19-Nov-2019, 11:27
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
19-Nov-2019, 12:40
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.

seven
19-Nov-2019, 12:47
coating issue, caused by ageing and some environmental factors like humidity perhaps. no fungus involved here.

Mark Sawyer
19-Nov-2019, 13:03
By the serial number, it's a late 1940s/early 1950s lens. Coatings of that time were softer and less well-bonded to the glass, so were more susceptible to mechanical and environmental damage. The internal coatings are more important for preventing internal reflections (which is where most flare comes from), and better protected, of course. From a practical standpoint, I wouldn't worry about it.

https://www.ground-glass.net/large-format/rodenstock-lenses-age