In article , Jeff Keller <jrk_om@xxxxxxxxxxx> writes
- ----- Original Message -----
From: "Kennedy McEwen" <rkm@xxxxxxxxxxxxxxxxxxxx>
Part of your own description of the problem with uncoated spectacles
indicates its source. To produce a ghost scene image on a single
element lens requires reflection from BOTH surfaces. Eliminate
reflection at either surface and the ghost scene image goes away.
Reflection from only one surface means you get a ghost image of your
eye, not the scene.
Light reflects off film hits back surface of lens, reflects back onto
film .... ?
No. The film is a diffuse, almost Lambertian, reflector, so any light
reflected from the film and subsequently from the lens back surface
would certainly not produce a ghost image. Also, for the same reason
and the distance of the film from te back lens surface, the amount of
light reaching the film through this route would be negligible, whether
the surface was coated or uncoated. You might just detect it if your
image comprised a couple of black spots on a bright white background but
otherwise the issue with coating on the back surface is specular
reflection from the surface back into the lens itself and thence onto
the film multiple reflections.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers
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