FROM: gbreault@aol.com (GBreault) SUBJECT: Re: Lens Cleaning DATE: 03 Jul 2000 20:39:13 GMT ORGANIZATION: AOL http://www.aol.com NEWSGROUPS: rec.photo.equipment.large-format >Subject: Re: Lens Cleaning >From: Dave Morrison dmorrison@sptimes.com >Date: 07/03/2000 9:10 AM Eastern Daylight Time >Message-id: <39609226.DA57174C@sptimes.com> > >Just a question about cleaners: What can a lens coating withstand? From the >list of various cleaning agents mentioned here, it sounds like lens coatings >are tougher than I had ever imagined. I had a college instructor who became >almost apoplectic if you used your breath to moisten a lens surface for >cleaning. I'll admit my breath isn't always a field of daisies, but it has >NEVER smelled like acetone. >dave >http://www.morrisonphotographics.com > Hi Dave, I work for a manufacturer of precision optical measurement systems. A few years ago I had the same question and asked a tech on the production floor to durability test a lens coating on 3 lenses with a dilute soap solution, methanol, and acetone. With the soap solution, the coating was damaged with 20 light swipes, and removed completely with 60. With both the other solutions, the coating was undamaged at over 100 swipes. Different coatings will yield different results, and some require different chemicals, but there are some general rules we use here. 1. Never, ever, wipe it dry. 2. Use air pressure and gravity first. 3. Try light pressure with a brush combined with air to loosen stubborn particles 4. When using liquid cleaners, 1 swipe wth a wetted tissue, then throw it out. 5. 1st use very very dilute soap in water to wash off the mud. DON'T SCRUB!!! 6. Methanol to wash off the soap and water films. DON'T SCRUB!!! 7. Use acetone to wash off the methanol film. DON'T SCRUB!!! Oh, did I mention not to scrub? Biggest problems we see are people trying to shortcut the process. Water will remove things that acetone won't budge. Too much soap is really really bad. Other problems are with old, contaminated chemicals, cruddy water, dirty tissues, and scrubbing. I have also been cleaning lenses for a lot of years, but it wasn't until I got here that I learned how to really clean them. Follow Richard's advice on the use of acetone, and the dragging technique works very well. I do have to diasgree about the Windex though. I wouldn't use it on a coated surface. Cheers Jerry Breault FROM: dickburk@ix.netcom.com (Richard Knoppow) SUBJECT: Re: Lens Cleaning DATE: Mon, 03 Jul 2000 22:40:28 GMT ORGANIZATION: MindSpring Enterprises NEWSGROUPS: rec.photo.equipment.large-format Dave Morrison wrote: >Just a question about cleaners: What can a lens coating withstand? From the >list of various cleaning agents mentioned here, it sounds like lens coatings >are tougher than I had ever imagined. I had a college instructor who became >almost apoplectic if you used your breath to moisten a lens surface for >cleaning. I'll admit my breath isn't always a field of daisies, but it has >NEVER smelled like acetone. >dave >http://www.morrisonphotographics.com > > >Richard Knoppow wrote: > > I've snipped the rather long thread. Anti-reflection coatings found on lenses made after about 1945 are vacuum deposited layers of dielectric materials like Magnesium flouride, Zinc sulfide, many others. Most single coated lenses are Magnesium flouride. These materials are fairly tough but the coatings are very thin and suseptible to mechanical damage. The coatings and optical glass are vulnerable to strong acids and alkalies. The acid in a finger print will etch both glass and coating if allowed to remain on it for any length of time. The best cleaner for general purposes is Kodak Lens Cleaner. This is a combination of diluted Ammonium carbonate and two surfactants, an ionic one and a non-ionic one. Windex can be used on some glass but it is Ammonium _hydroxide_ as is houshold ammonia. It has a much higher pH than the carbonate so is more likely to dissolve a very thin layer of coating or glass. Reagent grade Acetone is a standard cleaner for optical assembly. It is a very effective solvent for oils and greases but will also dissolve paint and many plastics. It is not recommended for routine cleaning. The reagent grade is necessary to avoid leaving a residue, the stuff from the paint store ususlly won't leave a clean surface. 1,1,1,Trichlorethane is a selective solvent, once commonly available in spray cans. It is an environmental hazard so is much harder to get now. It is useful as a de-greaser because it won't dissolve most paint or harm most plastics. This, like the acetone, is an emergency cleaner. Very pure Isopropyl alcohol can also be used as a degreaser. Most drug stores carry 91%. This works as a mild degreaser. Isopropyl alcohol absorbs moisture readily so getting purer than 91% becomes a packaging problem. The general rule is to use the mildest cleaner, and not to clean any more often than necessary. Use lens caps to protect the surfaces from dirt and damage. Any cleaner should be applied with a grit-free tissue or cloth. I like Kimwipes, which are a lintless tissue intended for this kind of use. Kodak Lens Tissue is also good but tends to disintegrate when wet. Tissues should be used once and tossed. By once, I mean put some cleaner on it, drag it over the lens, toss it. Use another tissue for the next application. Kodak lens tissue is particularly good for making one-time-use brushes. Roll the tissue into a tube. Fold it in half, tear the resulting double tube in half and fold it over so that the torn ends are together. Tearing them will have feathered the tissue. Use the featherd end as a brush to pick up dust. Again, use it once and toss it. Ordinary tissue paper and toilet tissue is apt to have grit in it. Its also good to have an air bulb which can be used for gently blowing off lenses. Canned air tends to be too forceful and to condense moisture on the lens surface. Some optical glass is actually water soluable and all glass corrodes to some degree. This is probably the reason for the proscription about breathing on the lens, because of the moisture in the breath. I rather think this is overkill. In general, the less you touch the surface of a lens the better. Possibly Helge Naried will add further comments. He has been involved with advanced optics and optical manufacture so has some real expertise in this area. --- Richard Knoppow Los Angeles, Ca. dickburk@ix.netcom.com FROM: "Robert E. Smith" SUBJECT: Re: Lens Cleaning DATE: Tue, 04 Jul 2000 08:33:07 -0400 ORGANIZATION: ..Lonesome Pine Engineering NEWSGROUPS: rec.photo.equipment.large-format Richard Knoppow wrote: > > Dave Morrison wrote: > > >Just a question about cleaners: What can a lens coating withstand? From the > >list of various cleaning agents mentioned here, it sounds like lens coatings > >are tougher than I had ever imagined. I had a college instructor who became > >almost apoplectic if you used your breath to moisten a lens surface for > >cleaning. I'll admit my breath isn't always a field of daisies, but it has > >NEVER smelled like acetone. > >dave > >http://www.morrisonphotographics.com > > > > > >Richard Knoppow wrote: > > > > > I've snipped the rather long thread. > > I, as well have eleminated some material not relevant to my specific focus of observation: > Kodak lens tissue is particularly good for making one-time-use > brushes. Roll the tissue into a tube. Fold it in half, tear the > resulting double tube in half and fold it over so that the torn ends > are together. Tearing them will have feathered the tissue. Use the > featherd end as a brush to pick up dust. Again, use it once and toss > it. > remaining advise also cut, sorry: It is gratifying to hear an expert comfirm a method which has been in here use since about 1975 when I purchased a Fujinon marine binocular. The manual stated the exact methode Richard refers to above. In addition, Fujinon suggests that you begin cleaning at the center of the lens working tward the edge with circular motion. I have been using this proceedure in lens cleaning ever since with mostly happy results. dr bob.