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What is the proper/recommended way to clean a lens?
Frank, as I said, lots of opinions on this one (mine included).
I think a lot of commercial lens cleaners are going to have some alcohol to encourage evaporation. ETC for example recommends a 50/50 mix alcohol to distilled water for cleaning the lenses in their lights (but most are not coated or barely coated).
I’m no chemist, but I think mostly the cautionary tales with alcohol and strong solvents is to not have the 75%, 91%, or 99% be your goto. And avoid applying all liquids directly, wet a lens tissue instead. But if a lens has a lot of oils or fingerprints some kind of weaker blend containing a solvent as in some commercial products or Rosco may be required. Though ammonia is definitely one to avoid (in solutions above 5%?). There is a huge gap between cleaning uncoated glass and cleaning coated lenses or porthole.
Worth noting, rosco is a lighting/theatre company too, and that product has been around for eons, so never “really” marketed towards modern camera/projection lenses, but that doesn’t mean it’s unsafe to use for stubborn situations, such as Mark’s citing of alcohol plus methyl ethyl ketone. Also worth noting almost zero of our analog lenses are “modern” either. ;-)
But overall, scratch damage risks are about the fabrics and the techniques. What solvent blends are ultimately safe for ALL coatings and rubber or plastic lens element mounts it a slightly deeper discussion. Safe occasionally? Safe regularly? Etc.
The best advice to care for our analog lenses probably has nothing to do with how to clean them, but recommendations to avoid touching the elements, use lens caps (with 3d printing none of us have excuses anymore), and store unmounted ones in a dust free relatively sealed container, perhaps with a desiccant if you have humidity problems. I should follow my own suggestion, we are good on 2 of 3. ;-)
As an aside, in college I worked in a clean room lithography lab related to the entertainment lighting industry. We cleaned all our glass substrates (even dichroic ones) with acetone before applying photo resist. Glass can handle most things, it's the proprietary coatings and element mountings that involves all the guess work and over abundance of caution. Considering what coatings exist on some of our film lenses are 20-50 years old too, veering in the direction as much caution as possible seems wise?
If you are feeling spendy and want to service a gross lens without touching it, consider one or more applications of this non-contact polymer cleaner? It's spendy but they seem to have the science backing up the product, NASA uses, etc.
That is the product we are considering to clean our optical periscope mirrors in situ, rather than yank them off and submersion clean them. TBD if the stuff is thick enough to apply to an inverted surface without making a mess. lol Top or both will probably have to come off I imagine... best applied to a horizontal surface.
For the sake of completeness, The Tiffen Brand lens cleaner in our booth is like 90% distilled water, and a tiny bit of surficant and denatured alcohol. It apparently has a tiny bit of ammonia hydroxide (ammonia solution) too...
So if we were going ammonia free even that would be out. The caution around ammonia and marketing of these things is confusing for sure. Ammonia having cleaners are generally considered unsafe for coatings, but Tiffen specifically markets it as safe for delicate coatings. Maybe it is all about the concentrations?
If one is inclined to trust our AI overlords, this is the advice regarding presence of ammonia hydroxide:
While many household cleaners with ammonia can damage lens coatings, Tiffen's brand lens cleaner is formulated to be safe. The product's safety data sheet reveals that ammonia hydroxide is present in a very low, diluted concentration, likely under 5%, and balanced with other ingredients.
Here's why Tiffen's cleaner is safe for coatings while other ammonia-based products are not:
Low concentration: Tiffen's lens cleaner uses a much lower concentration of ammonia than household cleaners. Strong ammonia solutions have a high pH level that can be highly corrosive to the delicate chemical layers of lens coatings, causing damage such as hazing, peeling, or corrosion over time.
Engineered formula: A consumer-grade cleaning product like Tiffen's is a complex chemical mixture, not just a single ingredient. It is engineered to use the detergent properties of ammonia for cleaning while counteracting the corrosive effects with other additives. This formulation allows for the effective removal of dirt and grime without harming the lens.
Manufacturer claims: Tiffen specifically advertises its lens cleaner as safe for all optical lenses, filters, and sensitive coatings. The company, which is an established name in professional optics, would not make this claim if the product caused damage when used as directed.
Circling back to technique, I think all the "wisdom" surrounding avoiding applying liquids directly to lenses has to do with avoiding runs and contamination into the lens body... not just the element mounting materials... plenty of camera and projection lenses have mechanical components that are intentionally lubricated, and getting a solvent in there might not only remove some needed lubrication somewhere, but risk spreading it around to internal optical elements too.
Atomizing or pouring a liquid onto a lens directly is not what causes damage, it's just a risky practice relative to the rest of the lens.
When I worked at Canon Service in Chicago, they mixed 93% alcohol and Methel Ethel Ketone 50/50 and we used that to clean optics. It evaporates very quickly and leaves no film.
When I worked at Canon Service in Chicago, they mixed 93% alcohol and Methel Ethel Ketone 50/50 and we used that to clean optics. It evaporates very quickly and leaves no film.
Mark, do you know what the motivation behind the cleaners marketed as "alcohol free" such as Film-Tech's cleaner are? Most commercial ones are gonna have some alcohol... is there any reason to be shy of alcohol for some reason? Maybe simply to make them safe for polycarbonate lenses and plastics too?
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