Re: [ATM] Flexed mirrors

["astroguy@nas.com" <astroguy@nas.com>]

You can make a paraboloid by changing the curve in many ways.  The most
common and easiest method is to parabolize the center of the mirror.

The flex design works in this way.  Flex design has been around for many
years and WORKS as proven by Bill Kelly and Alan Adler.   Mr. Adler gave a
great presentation on flex mirror technology and design several years ago
at the Telescope/Optics workshop.  His computerized program and design
parameters were very convincing and a real sample at the workshop made for
proven technology.  To this day, i am still surprised that more flex
mirrors are not being produced.

Compared to melting glass, microwave kilns, alternative substrates, etc.,
flex mirrors are EASY!!!!

Just my 2 cents,  Kreig



Original Message:
-----------------
From: Christopher Todd christopher.todd@gmail.com
Date: Mon, 14 Jan 2008 19:29:36 -0500
To: atm@atmlist.net
Subject: Re: [ATM] Flexed mirrors


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

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