Aggressive Chemicals and Lens Coatings

T42 · Dec 23, 2014

Hello APUG Forum.

I am trying to learn what chemicals will harm or strip modern lens coatings from camera lenses, or will otherwise render an optic damaged from their contact or use on the lens's coatings. I want to learn whatever chemicals should NOT be used to clean lenses at all, because they will damage, stain, strip, or otherwise harm lens coatings or lens elements to which they are applied.

Also, I would like to get a sense of acceptable chemicals to use to clean a lens, in order of their relative aggressiveness, cautions, and applications.

For example, imagine that we have a really, really tough contaminant, such as getting tar onto a lens (not that I have). What solvents could we use to remove the tar and clean the optic without running a serious risk of harming the lens or its coatings?

Would you know of some resource to learn more about this? What I see on the net is mostly the basic "here's how to clean a lens" stuff for dust and basic spots, fingerprints, kiddie smudges, etc.

Many thanks.

Henry

nsurit · Dec 23, 2014

I've used denatured alcohol for years. I'm sure some might disagree with this approach and I can't see that it has ever harmed a lens. Bill Barber

02Pilot · Dec 23, 2014

After removing obvious loose dirt and grit with a blower, I start with basic household glass cleaner. If that doesn't work, I move up to 95% rubbing alcohol, then Ronsonol, then Flitz metal polish. I've never had to go any more aggressive than that. All were applied with clean cotton swabs, and the lens was cleaned with regular glass cleaner afterwards. I've used all of the above on numerous post-war lenses without issue; I would hesitate to use them on coated pre-war lenses, which are often fragile.

snapguy · Dec 23, 2014

back when

Back in the day, a lot of press photographers used to clean the lens on their Speed Graphics with the tip of their necktie but I suppose you don't want to hear about that. I suspect camera lenses are not the hothouse flowers you seem to think they are.

flavio81 · Dec 23, 2014

Coatings will be resilient against almost anything except perhaps hydrofluoric acid or some really really strong substance.

What damages the coatings are rubbing over the lens while abrasive particles like dirt or sand are present.

Alcohol is just OK.

Athiril · Dec 23, 2014

Cleaned some fungus off a lens really that had a snow-flake type fractal kinda pattern, alcohol wouldn't budge it, I'm guessing people would have tried to say it etched into the coating, but windex cleaned it right up no probs.

Gerald C Koch · Dec 23, 2014

Kodak one made a very good lens cleaner. I purchased a lifetime supply (a pint bottle) many years ago. I personally would not use any liquid that is not approved for use on lenses. While coatings have improved since their first use I believe that they are still softer than the actual glass. Remember these coating are VERY thin sometimes only a few atoms thick.

Arklatexian · Dec 24, 2014

02Pilot said:
After removing obvious loose dirt and grit with a blower, I start with basic household glass cleaner. If that doesn't work, I move up to 95% rubbing alcohol, then Ronsonol, then Flitz metal polish. I've never had to go any more aggressive than that. All were applied with clean cotton swabs, and the lens was cleaned with regular glass cleaner afterwards. I've used all of the above on numerous post-war lenses without issue; I would hesitate to use them on coated pre-war lenses, which are often fragile.

A mention was made about tar on a lens. The only one of your cleaners that would remove tar is the Ronsonol (is that the same as lighter fluid?) or some other petroleum-based liquid. I was taught that alcohol is not a solvent for petroleum-based products. Now I have a question: which lenses were coated prior to World War 2? I am assuming that is the war that you referred to. This question is not to be taken as anything other than for information for me.......Regards

Xmas · Dec 24, 2014

coating or Blooming was known about from 19th century but Zeiss had the first practical process as a military patent secret just before WWII so 88mm anti air gun sights and contax II Sonnars.

Xmas · Dec 24, 2014

T42 said:
Hello APUG Forum.

I am trying to learn what chemicals will harm or strip modern lens coatings from camera lenses, or will otherwise render an optic damaged from their contact or use on the lens's coatings. I want to learn whatever chemicals should NOT be used to clean lenses at all, because they will damage, stain, strip, or otherwise harm lens coatings or lens elements to which they are applied.

Also, I would like to get a sense of acceptable chemicals to use to clean a lens, in order of their relative aggressiveness, cautions, and applications.

For example, imagine that we have a really, really tough contaminant, such as getting tar onto a lens (not that I have). What solvents could we use to remove the tar and clean the optic without running a serious risk of harming the lens or its coatings?

Would you know of some resource to learn more about this? What I see on the net is mostly the basic "here's how to clean a lens" stuff for dust and basic spots, fingerprints, kiddie smudges, etc.

Many thanks.

Henry

It is simpler to screw on a uV filter to protect from sea gulls.
Followed by a generic rubber lens hood to protect from side walk slabs.
Not all lens coatings are hard coatings.
Don't expect to remove a finger print from a multi coated filter.
So resist the temptations of Lucifer don't clean your lenses.
Optical glass is not like window glass forget about windex.

RalphLambrecht · Dec 24, 2014

02Pilot said:
After removing obvious loose dirt and grit with a blower, I start with basic household glass cleaner. If that doesn't work, I move up to 95% rubbing alcohol, then Ronsonol, then Flitz metal polish. I've never had to go any more aggressive than that. All were applied with clean cotton swabs, and the lens was cleaned with regular glass cleaner afterwards. I've used all of the above on numerous post-war lenses without issue; I would hesitate to use them on coated pre-war lenses, which are often fragile.

That's a very good approach.I use medical alcohol after cleaning withwallgreen's lens cleaner for eye ware.I t costs little and you get free refills.Just go to their eye-ware section.

Nodda Duma · Dec 24, 2014

I've cleaned a lens once or twice during my career and can provide some insight:

In optical shops and during lens assembly I've used the following listed in the order of most used:

-Acetone
-Isopropyl Alcohol
-Methanol
-Recipe from Arkansas Sky Observatory
-Denatured Alcohol
-Windex

I think you'll find most opticians will agree with that list (at least the first three). I would not use the first two for lenses in plastic or painted barrels.

All anti-reflection coatings that I know of will survive Moderate Abrasion Resistance testing as called out in MIL-PRF-13830 (you can google this and read the test). That includes the earliest of coatings, which are single-layer MgF2 (mag fluoride). (Fun fact: magnesium flouride lenses do not need coating).

The most fragile coatings I know of is basic silvered telescope mirrors. That is much more fragile than anything you'll see on refractive lenses. Those I do not clean unless I absolutely have to, and when I do the ONLY cleaner I will ever use is the Arkansas Sky Observatory recipe..and only if running under warm water and messaging the surface with soap on clean fingers will not do the job.

In fact, I do not clean any lens surface unless I absolutely have to. Make no mistake: the single most damaging operation you can perform to an optical surface (short of outright neglect or abuse) is to clean it. Coatings are not necessarily softer than glass. Compare knoop hardness of MgF2 to optical glass for example. But the coatings will wear down from cleaning (think about how polishing works).

Another fun fact: you have to obscure ~13% of an optical surface to have an affect on the MTF. That is A LOT of dust. If you're cleaning to remove specs of dust because they bother you...don't.

Clean fingerprints as soon as possible. The mild acid in your skin oils will etch the coating and glass.

benjiboy · Dec 24, 2014

This is the best lens cleaning fluid I have ever used and I highly recommend it http://www.bhphotovideo.com/c/produ...Solutions_EC_Eclipse_Optic_Lens_Cleaning.html

Dan Fromm · Dec 24, 2014

oldtimermetoo said:
Now I have a question: which lenses were coated prior to World War 2? I am assuming that is the war that you referred to. This question is not to be taken as anything other than for information for me.......Regards

Practically speaking, none for the general public. Hard coating (MgF, mentioned elsewhere in this discussion) for lenses sold to civilians began late in WW-II, was in general use around 1947. Re late WW-II, I had a Cooke Aviar made in 1944 that was hard coated, eventually gave it to Jim Galli, who likes Aviars. In the US, EKCo started hard coating in late '46. I have an uncoated 101/4.5 Ektar made in '46, have seen coated 101/4.5s made later that year. Some makers coated some but not all of their lenses. I have three f/14 Perigraphes from the late '40s and 1950, none appears to be coated, also a 1950 f/6.8 Perigraphe that is. Yes, I know, appearances can be deceiving.

Xmas · Dec 24, 2014

Nodda Duma said:
That includes the earliest of coatings, which are single-layer MgF2 (mag fluoride). (Fun fact: magnesium flouride lenses do not need coating).

Neither statements are true

Some of the early coatings did not use the Zeiss MgF2 process!
MgF2 optics will be improved by coating, need is another matter I'll give you.

The syndrome in this thread is CCD

Compulsive Cleaning Disorder, dont finger print them either

Dropping a lens without filter and lens hood + camera or back cap is worse again but many people manage that... I have lots of samples that people have given me...

Noel

Nodda Duma · Dec 24, 2014

Funny Xmas...I suppose I could be technical and specify the earliest practical AR coatings were MgF2. The earliest coatings in general were, of course, silver for mirrors.

Riddle me this: what material would you coat a Mag Flouride lens with which has an index of refraction between that of MgF2 and air? Water?

I've never known anyone to bother coating MgF2 in their optical designs. Not saying you couldn't do it I suppose..maybe some professor would do it just to say they had. Just haven't seen anyone bother. The Tx is high and the index is low...especially in the infrared spectrum where the material sees use. The gain isn't worth the added cost.

Xmas · Dec 24, 2014

Nodda Duma said:
Funny Xmas...I suppose I could be technical and specify the earliest practical AR coatings were MgF2. The earliest coatings in general were, of course, silver for mirrors.

I should have been more specific sorry
I think that Leitz did not use the Zeiss process cause it was a Ge patent (at least initially) their type I Summicrons are well easy to scratch...
The Blooming technique was known about in the 19th century
http://www.filmshooting.com/scripts/forum/viewtopic.php?f=1&t=24573
They were aware of how it worked so the link is a bit abstract.

Nodda Duma said:
Riddle me this: what material would you coat a Mag Flouride lens with which has an index of refraction between that of MgF2 and air? Water?

I've never known anyone to bother coating MgF2 in their optical designs. Not saying you couldn't do it I suppose..maybe some professor would do it just to say they had. Just haven't seen anyone bother. The Tx is high and the index is low...especially in the infrared spectrum where the material sees use. The gain isn't worth the added cost.

I tried to phrase it carefully, the need with a low refractive element is much less, but I believe it is possible with the modern layered multi coating process, which have a rough micro surface. this is one of the reasons why many multi coated filters are impossible to degrease... YMMV.

I think the blooming linked above worked by selective etching due to weathering of optical glass... the modern multi coating can emulate this, so rough coating MgF2 would work?

The transmission in uV is resonable to BTW.

Nodda Duma · Dec 24, 2014

I've seen coating layers with intentional rough surfaces in order to allow subsequent layers to be applied without delamination. The most common application is diamond-like coatings on Cleartran/ZnS to provide better protection against environmental damage, but that's not necessarily an AR coating and it is covered by a top layer to avoid the very issues you mention above (Infrared Domes and Materials by D. Harris). I'd be more apt to believe that a rough top layer was from poor QC or an unintentional deposit after the lens shipped.

The 1809s coatings worked because the optical glass of the time oxidized and created a thin surface layer of tarnish basically. The tarnish had a lower index than the glass, reducing the index deltas at the interface. If it was the proper thickness then you'd get a reduction in reflection. I'm not sure that's a very controllable process. At least, no one I'm aware of coats lenses these days using that method (vapor deposition / sputtering methods are controllable and work faster).

Multilayer coatings can be degreased easily enough? Optical shops do it every day as a final cleaning step...usually with acetone.

Multilayer coatings are a controlled build-up of multiple layers of different materials designed to provide a specified reflection (or transmission) in a specified spectral band. The layer thicknesses and the material are the variables the coating designer uses to set the reflection. Inevitably, the top layer is Magnesium Flouride because no other optical material has an index as close to that of air.

In any case the discussion is kind of academic. MgF2 optical elements are used in the infrared spectrum and typically CaF2 or LiF is used instead...either way the material is much too expensive to be used for visible film cameras.

Fun discussion. Merry Xmas

Jim Noel · Dec 24, 2014

Xmas said:
It is simpler to screw on a uV filter to protect from sea gulls.
Why put a piece of cheap glass, very likely not optically flat, in front of a several hundred o thousand dollar lens.
Followed by a generic rubber lens hood to protect from side walk slabs.
A metal hood will be far more protection against drops.
Not all lens coatings are hard coatings.
True.
Don't expect to remove a finger print from a multi coated filter.
Why not? I used to do it for my students at nearly every class session.
So resist the temptations of Lucifer don't clean your lenses.
Better yet, don't put your fingers or other things onthem.
Optical glass is not like window glass forget about windex.

Or any other liquid.

Activated charcoal will remove just about anything that might get on your lens. Buy it in capsules at a health food store. Empty a few capsules into a 35m film cannister. Dip a cotton swab in the powder, knock off as much as possible and then use it to clean the lens by lightly rubbing it on the lens in circles beginning n the center and working your way out. Your lens wil sparkle with no danger of liquid getting between the elements.

By the way, neckties used to be made of silk and thus were soft and safe to use on lenses.

E. von Hoegh · Dec 24, 2014

Jim Noel said:
Or any other liquid.

Activated charcoal will remove just about anything that might get on your lens. Buy it in capsules at a health food store. Empty a few capsules into a 35m film cannister. Dip a cotton swab in the powder, knock off as much as possible and then use it to clean the lens by lightly rubbing it on the lens in circles beginning n the center and working your way out. Your lens wil sparkle with no danger of liquid getting between the elements.

By the way, neckties used to be made of silk and thus were soft and safe to use on lenses.

Until they got contaminated with grit.
It's far better to keep your lens clean, than to keep cleaning it.

E. von Hoegh · Dec 24, 2014

Nodda Duma said:
I've seen coating layers with intentional rough surfaces in order to allow subsequent layers to be applied without delamination. The most common application is diamond-like coatings on Cleartran/ZnS to provide better protection against environmental damage, but that's not necessarily an AR coating and it is covered by a top layer to avoid the very issues you mention above (Infrared Domes and Materials by D. Harris). I'd be more apt to believe that a rough top layer was from poor QC or an unintentional deposit after the lens shipped.

The 1809s coatings worked because the optical glass of the time oxidized and created a thin surface layer of tarnish basically. The tarnish had a lower index than the glass, reducing the index deltas at the interface. If it was the proper thickness then you'd get a reduction in reflection. I'm not sure that's a very controllable process. At least, no one I'm aware of coats lenses these days using that method (vapor deposition / sputtering methods are controllable and work faster).

Multilayer coatings can be degreased easily enough? Optical shops do it every day as a final cleaning step...usually with acetone.

Multilayer coatings are a controlled build-up of multiple layers of different materials designed to provide a specified reflection (or transmission) in a specified spectral band. The layer thicknesses and the material are the variables the coating designer uses to set the reflection. Inevitably, the top layer is Magnesium Flouride because no other optical material has an index as close to that of air.

In any case the discussion is kind of academic. MgF2 optical elements are used in the infrared spectrum and typically CaF2 or LiF is used instead...either way the material is much too expensive to be used for visible film cameras.

Fun discussion. Merry Xmas

I have a 6" Goerz Dagor from 1906-08, the outer surfaces have a gorgeous purple bloom. It looks coated but isn't, there's nothing on the inside surfaces - where it would do some good. I did a comparison with it and a 150 Convertible Symmar (single coated) the contrast was about the same. In fact if I hadn't numbered the 4x5 transparencies I doubt I could have told them apart.

Dan Fromm · Dec 24, 2014

E., the bloom on the outer surfaces improves transmission.

flavio81 · Dec 24, 2014

Modern (ca. 1963-) coatings are invariably hard coatings and are very hard and resilient to many many substances.

I've yet to damage a coating.

Kirks518 · Dec 25, 2014

snapguy said:
Back in the day, a lot of press photographers used to clean the lens on their Speed Graphics with the tip of their necktie but I suppose you don't want to hear about that. I suspect camera lenses are not the hothouse flowers you seem to think they are.

In an old camera manual (pretty sure it was Kodak), it said to breathe on the lens, and rub gently with your shirt/t-shirt/necktie (can't remember which), and then if additional cleaning is necessary, to use the Kodak Lens Cleaning Fluid and Kodak Lens Tissue.

I start by blowing off any loose stuff, then a light brushing, then lens tissue with lens cleaning fluid. If that doesn't work, then I go to a lenspen, or more vigorous rubbing with the tissue or my shirt. I haven't scratched a lens, or the coatings yet. I actually tried to damage coatings on a junker lens with 'normal' cleaning supplies, and couldn't do it. I have, however, left cleaning marks on a pre-war uncoated lens.

E. von Hoegh · Dec 27, 2014

Dan Fromm said:
E., the bloom on the outer surfaces improves transmission.

Yes it does. But, it does nothing to reduce internal reflections - not that there is much of a problem with only two internal surfaces.

Aggressive Chemicals and Lens Coatings

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