Re: Magnesium Flouride

[Bernard Cleyet <anngeorg@PACBELL.NET>]

I've found the Melles Griot catalog more useful educationally than for
ordering (they're damned expensive;  I use Rolyn when possible).  Like
the Canberra catalog, they preface each section with some practical
Physics.

Defocused ghost images:

http://www.mellesgriot.com/products/optics/oc_1.htm

bc, who did write it was "very important".


Michael Edmiston wrote:

> Most people mention that AR coatings, especially on multielement lenses,
> allow higher transmission.  While this is true, I don't believe it is
> the major goal.  Bernard Cleyet came close to mentioning the major goal
> when he briefly mentioned lens flare.
>
> Lens flare is a gross example of a more subtle problem that grows to a
> major problem in lenses with many surfaces... loss of image contrast,
> also known as a fogged image.
>
> Light reflected from any len surface(s) and ultimately going out of the
> camera is a minor problem.  It just means we need a longer exposure to
> compensate for the lost of light.
>
> However, light reflected from any lens surface(s) and ultimately going
> into the camera and hitting the film or the CCD is light that not part
> of the image.  Non-image light that hits the film is like background or
> noise.  It just "fogs the film."  The most notable result is loss of
> contrast.  This can be subtle, or more severe such as a foggy picture,
> or distinct such as a visible flare.
>
> I understand that the fantastic zoom lenses the video cameras used by
> the major networks for football games, etc. would be totally useless
> without antireflection coatings on all the surfaces.  These lenses have
> so many surfaces that multiple reflections ending up as "fog" would make
> the image unusable.
>
>
> Michael D. Edmiston, Ph.D.
> Professor of Physics and Chemistry
> Bluffton College
> Bluffton, OH 45817
> (419)-358-3270
> edmiston@bluffton.edu