Aggressive Chemicals and Lens Coatings

[Bosaiya]

High percentage (+90%) rubbing alcohol from the drugstore is cheap, effective, and cleans itself up.

 

[Nodda Duma]

High percentage (+90%) rubbing alcohol from the drugstore is cheap, effective, and cleans itself up.

Here is the residue from 91% rubbing alcohol, magnified on an optical surface (ignore the round pits in the coating...a separate issue due to exposure to the environment).

That was on a surface cleaned by someone extremely anal about cleaning optics, done in a clean room to settle a bet about doing specifically what you suggest.

Those streaks from the other 9% of "stuff" in non-lab-grade isopropyl are very difficult to see, much less eliminate unless you have other ingredients in your cleaning solution.

The streaks will scatter light and reduce your contrast.

Use acetone if it's just glass and no barrel or blackening ink), lab-grade isopropyl, or windex filtered through a coffee filter. My recommendation for home use: the Arkansas sky observatory recipe and directions.

 

[Bosaiya]

Nice! It still looks a lot cleaner than any of my lenses. I mostly use the t-shirt method.

 

[pdeeh]

My recommendation for home use: the Arkansas sky observatory recipe and directions.

Just for interest's sake, I looked it up and it can be found here Dead Link Removed

It specifies a particular US product (Windex "blue") which I've never seen in the UK, but of course might be available elsewhere, plus quantities are given in US measures so would need conversion.

I'm in the huff-on-it-and-rub-it-with-my-sleeve school, of course, but then I'm a bit of a Neanderthal about these things

 

[Nodda Duma]

Nice! It still looks a lot cleaner than any of my lenses. I mostly use the t-shirt method.

Which is perfectly acceptable if you don't worry about resale value. I use the T-Shirt technique myself for my own stuff...just not at work.

 

[Nodda Duma]

Just for interest's sake, I looked it up and it can be found here Dead Link Removed

It specifies a particular US product (Windex "blue") which I've never seen in the UK, but of course might be available elsewhere, plus quantities are given in US measures so would need conversion.

I'm in the huff-on-it-and-rub-it-with-my-sleeve school, of course, but then I'm a bit of a Neanderthal about these things

Try Halford's auto glass cleaner or order windex off amazon. Windex contains ammonia, so you'd get close with an ammonia-based glass cleaner.

http://www.printerknowledge.com/thr...oblems-is-this-the-end.3980/page-2#post-27991

 

[Jim Jones]

In the field I've too often used the huff-on-it-and-wipe-with-whatever method, and as a result have had to replace an Ektar 203mm f/7.7 and a 50mm Summicron, two of my favorite lenses. Sometimes getting the shot is more important than risking the equipment; sometimes not.

 

[Bosaiya]

I've always put cameras and their accessories into the "tools to be used and eventually replaced" category, just like most other tools. I try to keep them in good working order but understand that they can and do wear out eventually. Wearing one out after much use and hopefully not too much abuse is a sign that you got a lot out of it. I don't think that's a bad thing.

 

[Bosaiya]

Does anyone have recommendations on what chemicals can be used to remove the coatings on lenses? I don't want to go the mechanical abrasion route because I know it won't be very even.

 

[Nodda Duma]

Does anyone have recommendations on what chemicals can be used to remove the coatings on lenses? I don't want to go the mechanical abrasion route because I know it won't be very even.

Coatings are stripped mechanically using pitch lap and polish. Optical coatings cannot be removed chemically (unless you select something that would destroy the glass substrate).

 

[Old-N-Feeble]

Coatings are stripped mechanically using pitch lap and polish. Optical coatings cannot be removed chemically (unless you select something that would destroy the glass substrate).

Does this include really old coatings from decades ago?

 

[Dan Fromm]

Does this include really old coatings from decades ago?

How many decades ago?

PMFJI, short answer: for most lens-makers post-1945 coatings are on to stay. Before that some makers' coatings on internal services may wipe off.

 

[Old-N-Feeble]

Dan, it was a somewhat generalized question but I thought it was focused well enough. I know coatings changed over the last many decades. I do appreciate your helpful reply.

 

[Nodda Duma]

Does this include really old coatings from decades ago?

Yes. Unless you're performing "mickey mouse" maintenance, you still must remove by mechanical means. The first single-layer coatings (not oxidation ie. blooming, let's be realistic) were MgF or MgF2, which is a crystalline material that dissolves as well as glass. You want to get rid of it without damaging the underlying surface and not degrade optical performance, strip it off by polishing it out.

 

[Old-N-Feeble]

Thank you, Nodda.

 

[Nodda Duma]

Thank you, Nodda.

My pleasure!

 

[benjiboy]

Why use "aggressive chemicals " there are so many excellent lens cleaning fluids for photographic lenses on the market that are perfectly safe and leave no residue I recommend this one it's magic. http://www.bhphotovideo.com/c/produ...Solutions_EC_Eclipse_Optic_Lens_Cleaning.html

 

[02Pilot]

Why use "aggressive chemicals " there are so many excellent lens cleaning fluids for photographic lenses on the market that are perfectly safe and leave no residue I recommend this one it's magic. http://www.bhphotovideo.com/c/produ...Solutions_EC_Eclipse_Optic_Lens_Cleaning.html

Because when you're rehabilitating a 50+ year old lens that's been indifferently treated and/or stored for much of that time, conventional chemicals are often rendered ineffective by the accumulated filth.

 

[benjiboy]

Because when you're rehabilitating a 50+ year old lens that's been indifferently treated and/or stored for much of that time, conventional chemicals are often rendered ineffective by the accumulated filth.

The O.P. stated "modern lens coatings" and made no reference to the type of optics you describe.

 

[Dan Fromm]

Because when you're rehabilitating a 50+ year old lens that's been indifferently treated and/or stored for much of that time, conventional chemicals are often rendered ineffective by the accumulated filth.

Modern coatings came in nearly 70 years ago. TTH started hard coating some lenses no later than 1944. EKCo began coating sometime in 1946. Coating was universal by 1950.

I had, gave to Jim Galli, a coated Aviar made in 1944. It wouldn't clean up well so I looked at it at 30x. The problem wasn't dirt, it was very fine pitting. I have several other lenses that just wouldn't clean up and, again, close examination found damaged glass, not dirt permanently adhered to the glass.

 

[Nodda Duma]

Dan I've seen the same thing (see post 27 above).

What I'm not sure is the exact failure mode. It's not a manufacturing defect like poor surface adhesion.. that would fail as a delamination or peeling off of the coating. My best guess is exposure to an environment that causes oxidation or dissolution of the coating layer and possibly the underlying substrate. The outer coating layer is often times MgF2 (magnesium flouride). So I looked up its chemical properties. Ever leave condensation on the lens? MgF2 is soluble in acid (fingerprints) and slightly soluble in water (0.0076 g/100g or 0.013 g/100g depending on reference). This isn't a lot but you're only talking a layer a few molecules thick. I've never looked into it fully but this may be a good reason to keep condensation off your coated optics! Especially in acidic atmosphere. Also why cleaning optics can be the most damaging action you can perform on an optical surface under normal use.

On lenses with this issue I've never known the full history of the lens. It appears to the eye as a haze that doesn't wipe off.

That pic was at 800x, by the way. Here is pitting at 80x



and 200x

 

[Old-N-Feeble]

Nodda, is it possible those spots are created by dust specs that were left on that lens for a very long time in a humid environment? I'm not suggesting mold or mildew damage but rather the erosion effects you mentioned. Things like dust and lint can absorb and hold moisture in one spot for a much longer time than on clean surfaces.

 

[Nodda Duma]

Nodda, is it possible those spots are created by dust specs that were left on that lens for a very long time in a humid environment? I'm not suggesting mold or mildew damage but rather the erosion effects you mentioned. Things like dust and lint can absorb and hold moisture in one spot for a much longer time than on clean surfaces.

Dust and lint could hold moisture to the surface, but I would think the spots would be few and far between and not so uniformly distributed or numerous. You'd see maybe a handful of spots. Keep in mind these are several hundred spots per square millimeter. Another thing to consider, the spots are so small they are similar in size to a cell (the living type) and round. Dust particulates look very different and would leave jagged pits and micro scratches from the resultant cleaning esp in this quantity. But maybe I suppose. I've seen stranger things. However my gut points to something more like condensation or misting.

 

[Old-N-Feeble]

Dust and lint could hold moisture to the surface, but I would think the spots would be few and far between and not so uniformly distributed or numerous. You'd see maybe a handful of spots. Keep in mind these are several hundred spots per square millimeter. Another thing to consider, the spots are so small they are similar in size to a cell (the living type) and round. Dust particulates look very different and would leave jagged pits and micro scratches from the resultant cleaning esp in this quantity. But maybe I suppose. I've seen stranger things. However my gut points to something more like condensation or misting.

I've seen lenses absolutely "coated" in dust. Extremely careful cleaning can successfully remove such debris without scratching with tremendous care/patience and lots of time. Unfortunately, my hands are too unsteady these days to risk damaging valuable optics if they're truly filthy.

 

[Mustafa Umut Sarac]

Best lens cleaner material is the dry co2.