To my (admittedly limited) knowledge, I believe AR coatings need to be on the front/rear surfaces of the lens to do much of their work. Some lenses also have internal lens groups AR coated, but I do not believe it can be sandwiched, because as I understand the optics, it is the glass to air surface and differences in defraction that causes the principle reflection to begin with.
I believe most AR coatings are actually a vaporized metallic material that is "coated" to the glass or plastic surface, but it is literally a couple of molecules or atoms thick. Certainly, some of them are vulnerable to harsh and caustic chemicals, like ammonia. I have seen (and owned) some pretty costly lenses and they have had AR coatings on the exposed "surfaces". Art Laurie Solomon wrote: > Without trying to question or second guess the Schneider guy, I suspect > that the reason for the recommendation without reservations was because > he was referring to Schneider lenses and they unlike some of the cheaper > prosumer lenses may not put their multicoatings on the outside surface > of the lens or lens elements where they can get scratched or effected by > strong chemical solutions. Some of the coatings may very well be > sandwiched between layers of glass in the lens or lens element so as to > be protected from direct contact with anything including cleaning > solutions. Cheaper lenses and other optics may put the coatings on the > front of the optics, the lens or lens element as if the coating was > merely painted on, although I suspect that they are actually baked on to > the surface in some manner, which may leave then susceptible to damage > from liquids and scratching. Since many scanners use internal front > surface mirrors, their reflective surfaces are open to easy damage from > scratching and chemical solutions as might be the various coated optics > that are used to focus the light on the sensor, since typically the > assumption is that the optics are internal to the scanner and not user > accessible thus in no need of more elaborate treatment as might be the > case for camera lenses whose front elements and often rear elements are > accessible to users. > > > ----Original Message---- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > [EMAIL PROTECTED] > Sent: Monday, August 08, 2005 8:39 AM > To: [EMAIL PROTECTED] > Subject: [filmscanners] Re: HP PhotsSmart - questions > > >>I was surprised, but the Schneider guy recommended the dilute >>Windex solution without any reservations. >> >>Mr. Bill >> >> >> >>Laurie Solomon wrote: >> >>>I would speculate that the impact that various dilutions of ammonia >>>and water or Windex with ammonia might have on optical surfaces... >> >>-------------------------------------------------------------- >>-------------------------- >>Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe >>filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) >>in the message title or body > > > > ---------------------------------------------------------------------------------------- Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body
