Re: Alternative mirror technologies, WAS ATM Liquid-mirror telescopes

[Richard Schwartz <richas@idt.net>]

Chuck Knight wrote:
> 
> > I could probably build a mylar
> > mirror for even less!  (Say, have you actually tried that vacuum
> > technique, or is it just theory?  I have a 14" embroidery hoop
> > that's just "screaming" for an experiment!  Why would it form a
> > parabola, specifically, instead of a spherical mirror?)
> 
> I've got a question.  I've seen occasional references to mylar
> film mirrors...pulled into a parabola with a vacuum.  What
> makes it take on a parabolic shape?

I don't know either!  It seems to me that it is no different from a
balloon, and we all know that balloons, acting under surface tension,
take a SPHERICAL shape, not paraboloidal.