[filmscanners] Re: AR coatings

["Arthur Entlich" <artistik@shaw.ca>]

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: filmscanners_owner@halftone.co.uk
> [mailto:filmscanners_owner@halftone.co.uk] On Behalf Of
> wbgilloolyjr@charter.net
> Sent: Monday, August 08, 2005 8:39 AM
> To: laurie@advancenet.net
> 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...
>>
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>
>
>

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