Etched/pitted lenses

[johnnyrod]

I've been cleaning up a Zeiss Contessa LBE with 50mm Tessar f2.8, the lens glass however had a bit of fungus on it. This came off easily enough with some ammonia and peroxide, but I think the glass has been etched or pitted by the fungus. It was in spots with the odd streak, and now when you shine a light through the open shutter you see sparkles on the lenses. No way to know if they were in the same positions of course, but I tried to get it under a microscope at work. Difficult to view something transparent! but the markings do seem to be pitting. Is it possible to do something about this? Maybe just soften the edges of the pits to prevent the sparkling? They are pretty small, just dots, so I don't think they'll have much effect on IQ otherwise. With clean lenses these little rangefinders can take great pictures, and the mechanics and meter are all fully working.

 

[Pherdinand]

Sure just take some sandpaper and soften those edges!😀D

 

[02Pilot]

Which element was affected? The closer to the film plane, the more likely it is to cause problems. In all likelihood, however, you won't notice anything at all except in the worst possible conditions. Just shoot it.

 

[Dan Daniel]

I've read about people putting black paint in scratches and such to prevent flare. Never tried it myself.

I would shoot some tests and see what happens.

 

[Dwig]

I've read about people putting black paint in scratches and such to prevent flare. ...

I've seen this done successfully on a front element scratch, on a telephoto where the front element never comes close to being in focus. On a wide angle lens, especially retrofocus WAs, this would only work on interior elements near the iris.

 

[johnnyrod]

I didn't know if someone was going to suggest cerium oxide or jeweller's rouge, something I know precious little about. The paint idea I've heard of before I think, how do you suggest I apply it? The front element is the worst, the middle a bit and the back I think isn't too bad, but you can see spots on all of them. The front of the front element is coated, the rest are plain.

 

[02Pilot]

If you start in with cerium oxide or similar polishing agents, you're going to start altering the shape of the elements unless you've got a rig to ensure the shape remains intact. It's overkill IMO. The most I'd do is polish with Flitz metal polish, which may remove the coating, but is an effective chemical polish.

Have you actually shot with this lens at all? You need to in order to see if cleaning is even necessary, as well as to have a baseline to compare to if you do indeed polish the glass further.

 

[johnnyrod]

Do you mean the liquid one? Not sure I can get it in the UK, we have Brasso and others. The only thing I was thinking in terms of abrasive polishing was not to "remove" the damage but to soften the sharp edges to reduce impact on IQ.

No I haven't shot anything with it; the shutter was too sticky to be usable. If I can do something with the lens then I'd like to do that now rather than waste a film; I've had a similar one of these and ended up with poor shots though the glass was noticeably worse so I'm possibly worrying a bit over it. Do you think I'll be able to gauge the IQ by putting some tape over the film plane and projecting the image onto it?

 

[Dante_Stella]

Back in the bad old days, moisture would seep under lens coatings, into rare earth glass. That glass would then corrode and "pop." Fungus doesn't eat glass, but the same conditions that led to fungus may have caused your pitting.

Dante

 

[02Pilot]

Do you mean the liquid one? Not sure I can get it in the UK, we have Brasso and others. The only thing I was thinking in terms of abrasive polishing was not to "remove" the damage but to soften the sharp edges to reduce impact on IQ.

No I haven't shot anything with it; the shutter was too sticky to be usable. If I can do something with the lens then I'd like to do that now rather than waste a film; I've had a similar one of these and ended up with poor shots though the glass was noticeably worse so I'm possibly worrying a bit over it. Do you think I'll be able to gauge the IQ by putting some tape over the film plane and projecting the image onto it?

Flitz is a cream and made in Germany; not sure about UK availability. Other silver polishes should be similar, but I can't say that with any certainty. I wouldn't bring an abrasive like cerium oxide anywhere near a lens I cared about without a proper rig to preserve the shape of the elements - too many possibilities for things to go horribly wrong.

No way you'll be able to gauge image quality with tape or even a proper ground glass. Shoot up a short roll on test subjects and at least get some idea of what's going on. If you develop your own it's easier (you can just shoot a fraction of the roll), but no matter what you need a baseline.

 

[colyn]

Fungus doesn't eat glass

Dante

True..

It does attack the lens coating and once the fungus destroys the coating the acid from the fungus etches the glass...

 

[stompyq]

True..

It does attack the lens coating and once the fungus destroys the coating the acid from the fungus etches the glass...

Fungus makes hydrofluoric acid? What other acids could etch glass? I've always found this claim hard to digest

 

[Dante_Stella]

Fungus makes hydrofluoric acid? What other acids could etch glass? I've always found this claim hard to digest

That's the waste excretion of fungus. The fluoride ions come from the lens coatings. That's why fungus doesn't grow on uncoated lenses (well, not easily). But etching (what you get from fungus) and pitting (what the OP is talking about) are not the same thing.

D

 

[Robbie Bedell]

Flitz is very abrasive. It took the hard chrome off one of my Leicas...beware..

 

[02Pilot]

Flitz is very abrasive. It took the hard chrome off one of my Leicas...beware..

Were you using it with a high-speed power tool!? Flitz - at least the version I have access to here in the States - seems to have absolutely no abrasives at all, being a chemical polish rather than abrasive one.

 

[BillBingham2]

If you can, move the bad part towards the top or bottom of the frame.

B2 (;->

 

[goamules]

... I think the glass has been etched or pitted by the fungus. It was in spots with the odd streak, and now when you shine a light through the open shutter you see sparkles on the lenses. No way to know if they were in the same positions of course, but I tried to get it under a microscope at work. Difficult to view something transparent! but the markings do seem to be pitting. Is it possible to do something about this? Maybe just soften the edges of the pits to prevent the sparkling? They are pretty small, just dots, so I don't think they'll have much effect on IQ otherwise. ....

How many pits? How big? Those are the important questions. Many old lenses have tiny bubbles in the glass, maybe 3-10 of them that cause no image problem. About that many tiny pits, or more that are smaller, will not be a problem. Trying to "polish down" to below the pit level will be impossible, and is a solution looking for a problem.

Now if you mean an overall haze, or hundreds of pits, that's a different matter. Those do cause a big loss in contrast. It's all about how much percentage of the glass is flawed. 1-2%, no worries. 50% hazed, big problem.

 

[colyn]

Fungus makes hydrofluoric acid? What other acids could etch glass? I've always found this claim hard to digest

I've used several different acids over the years in glass etching..

 

[johnnyrod]

First of all, thanks for the many replies, it never ceases to amaze me what you guys (and girls) know.

Bill - no, markings are all over, and it's front cell focus so rotates!

Colyn - depends on the glass I guess but being vitreous it doesn't etch easily with acids unless augmented by other things like fluorinated compounds e.g. ammonium fluoride (which with strong acids gives HF). In a lab you'll only see a plastic stopper in a bottle of caustic soda and the rest are glass, as only sodium hydroxide (potassium hydroxide etc. too, obviously) will attack the glass surface and freeze the stopper in.

O2 pilot, thanks for the info. I feel a bit silly asking these questions but I don't have so much experience of the "is this normal?" kind. Re. coverage, check this out:
Contessa LBE lens with spots by John Rodriguez, on Flickr
Not easy to photograph but I think it shows every little mark. I inspected again this morning, the front of the front cell is by far the worst, the middle element seems fine, and the rear element isn't too bad, maybe a few marks on its rear surface. The frontmost surface is coated (the one in the outside world), the middle element looks uncoated, and I couldn't decide if there was some coating on the film-facing side of the rear element. If so then it's the coated surfaces that have taken the beating. There is a little haze around the edges of the front element too but nothing too bad. To complete the picture, this camera is from the mid/late-60s and would be pitched as an enthusiast's camera I think, so not a budget one but not a pro tool either. I mention that because maybe this helps make some sense of the glass/coatings that would have been used to make it.

 

[02Pilot]

From the photo, I'd say the haze around the edges is going to have a far, far greater effect that those tiny pits, especially since they're mostly on the front element. Clean it thoroughly to the extent possible and shoot.