Re: [ATM] Metallic Mirrors Vol 9, Issue 20

[Woodchuck <djv@bedford.net>]

On Mon, 20 Sep 2004 artbianconi@blast.net wrote:

> In the past I thought what it might be like,  making a parabolic
> mirror out of molten glass, using centrifugal force to generate
> the curve.
>
> Pour the lava like stuff on a rotating platen and let the
> centrifugal force "stretch" the glass into a concave meniscus. I
> have not a clue if anyone has ever made a mirror that way.
>
> Then I saw these posts on metallic mirrors and wondered what it
> would be like to spin a quart of room temp mercury into a
> parabolic shape. Change the f stop by speeding up or slowing down
> the "dish"! I wonder if mercury would be reflective enough.

Yes...  It works, it generates a parabola, and it's been tried in
some fairly large sizes, in the 1930's.  These experiments are
reported in the ATM series from Scientific American, if memory serves.

The problem is getting the drive steady, so that the surface doesn't
jiggle and ripple.

This is largely impractical for a curved mirror, but it has seen
practical application for large flats, no motor needed.

Other liquids (oil) have also been used for flats.

Dave
-- 
   "If large numbers of people believe in freedom of speech, there
   will be freedom of speech even if the law forbids it; if public
   opinion is sluggish, inconvenient minorities will be persecuted,
   even if laws exist to protect them."  -- George Orwell

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