Re: [ATM] Flexed mirrors

["Christopher Todd" <christopher.todd@gmail.com>]

I am sure I must be misunderstanding how this works, as I have never ground
my own mirror or seen a flexed mirror scope, so perhaps one of you could
correct me.

In comparing a paraboloidal mirror to a spherical one, am I correct in
understanding that the sagitta of the paraboloid will be smaller?  That is,
if you imagined a spherical mirror made of rubber and simply pushed down at
the edges, you could get a paraboloid?  So when you're figuring a
paraboloid, you are essentially grinding down the edges more than the
center? (apologies if this is a poor description, as I said, I've never
pushed glass)

But don't most flexed mirror designs place a firm base at the back edges of
the mirror (e.g., a truck tire rim, as described in Guy's message), and then
pull back on the center of the mirror?  Wouldn't that give you an oblate
ellipsoid?  (I am now geometry expert, but I am looking at figure 20.1 Conic
sections from Rutten and van Venrooij as I write this)  In order to get a
paraboloid, wouldn't you need to do the opposite - pull back at the edges
(or push up in the center)?

Confused,
Chris Todd

_______________________________________________
ATM mailing list http://www.atmlist.net/