>I wonder though... Is there such a thing as a
>"pseudo-half-silvered" mirror? Make one that applys
>the silver to a glass carrier and then applies a very
>thin protective film to the silver. While there still
>would be two reflections present they could be very
>close to each other, making the resulting beam be for
>all practical purposes a single beam.

The descan mirrors used in the space craft instruments I am dealing with are
done this way. I do not know what the protective coating over the silver is,
but there is certainly an extremely thin coating on top of the silver to
protect from tarnishing while still earth bound.

I suspect that if you went out and purchased a front silvered mirror, it
would come with such a coating as a normal finish.

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