Stubborn lens haze

[OlivierAOP]

I'm trying to remove some strange haze on a Mamiya Sekor 55mm (TLR). On the front element, appears to be on the inside surface. Here is a pic with boosted contrast to exaggerate the problem. I've tried lens cleaner, lighter fuel and methyl hydrate and it doesn't come off. The viewing lens has a similar haze. Any suggestions?


DSCF6966-1 by Olivier, on Flickr

 

[charjohncarter]

That is stubborn>

 

[OlivierAOP]

Just came off an overnight acetone bath... no change 🙁

 

[02Pilot]

If it's resisting chemical cleaning, the glass is probably etched or otherwise damaged. At this point, you will have to step up to mechanical cleaning. Start with something mild like Bon Ami cleaner (it's made from eggshells). If that doesn't do it, then you have to move to the nuclear option. Get some cerium oxide, make a paste by mixing with water, and very, very gently polish the surface. Working slowly and evenly, and checking frequently, you will take the damaged layer off and be left with clean glass.


I've revived horribly damaged glass with cerium oxide - scratched so badly it was translucent - so it should take care of the problem you have, but it is aggressive, so be careful.

 

[Ronald M]

Ultra sonic cleaning, abrasive anything will take off coating.

 

[shawn]

You can get premixed cerium oxide paste on Amazon in different article sizes. I have Glass Polish in 1.2um and it worked well to hand polish out some marks on a lens.

Shawn

 

[OlivierAOP]

Thanks all. I've also received advice to bake the lens then use lye. For polishing I could cast a mould of the surface with epoxy then put grit between mould & lens and polish... We'll see.

 

[02Pilot]

Baking the lens risks separating the elements. When I've done lenses if done it freehand but methodically - so many movements in such a way, turn the lens, repeat. For the kind of surface issue you have I suspect the creating a mold is unnecessary.

 

[OlivierAOP]

Upon closer inspection the deposit is on the outside surface. Rear element has some as well but it's less apparent and I haven't removed it to inspect. So maybe fire/smoke damage?

It's a singlet element so baking should be ok?

 

[02Pilot]

You can try it, but I'd certainly pack it in sand or something to make sure it heats and cools slowly and evenly, and doesn't crack. I'm not really sure what baking is supposed to achieve, especially if the damage was caused by heat in the first place.

I still say you're going to have to remove it mechanically.

 

[OlivierAOP]

I figured maybe the stuff would burn off, but it didn't. Lye didn't do anything either.

A repolish looks indeed necessary. I tested the lens on full-fame digital and the images have haze and bloom, but contrast can be restored via processing. Before going nuclear I'll see if the scanned film images hold up. When developers reopen that is.

Thanks again.

 

[Particular]

I just last week was working on a 65mm mamiya tlr lens that had similar haze. I think it must be a particular coating they used that hasn't aged well, because I have seen several of the same lenses for sale that look like they have the same problem. It was on an inside surface and was totally opaque. The surface had become dull. I tried the usual cleaning methods with no result. I then watched some youtube videos of people doing brutal polishing of lens elements to take the coating off using abrasives and dremels and what not.

I decided to do it a little more gently and start with toothpaste. I used a cotton bud and slightly wet toothpaste and drew circles on the glass. I noticed some improvement so I continued and after 10-15 it was totally clear! The good news was that the haze came off but I still have the coating. The bad news is that the other side of the hazy element is laminated to another cell. Presumably it is the same coating problem so there is some haze in between the cells that I can't get at. It is much less than what I removed, so I have usable, nice, slightly soft lens while previously it was just opaque and unusable.

 

[OlivierAOP]

Update. Made an epoxy mould for the outside surface, added grooves and polished the lens with 1.2 micron CeO2 for ~30m. It worked! Deposit came off on the periphery first, then on centre. Contrast/bloom is way better, sharpness seems unaffected. Did draw some scratches however, maybe I didn't clean up the grooves properly.

@CNNY. I think my situation was different? Haze was on the outside, and the images where somewhat usable as-is.


Edit: AR coating seems intact. Yellow tint on the surface is still present.

 

[02Pilot]

Glad to hear you were successful. You may be able to address the remaining scratches with very gentle polishing without the mold, but it may not be worth the effort (that's up to you).