Re: [ATM] 7 inch sphereical mirror

["Jerry" <wa4guu@verizon.net>]

I'm not a math wizard but the answer is rather simple isn't it?
There are few absolutely perfect mirrors if any at all. So we describe
mirrors as being a parabola or sphere (or other shape) within some
tolerances.

The 7" f:10 sphere (perfect) has about 86nm PV wave-front error from a
perfect parabola (assuming 550 nm wavelength). If your tolerance was 1/4
wave PV (137.5 nm) then you have 51.5 nm or just a little more than 1/11
wave of tolerance on the oblate side of the sphere to remain within 1/4 wave
of the parabola. You have 223.5 nm, a little less than half a wave of
tolerance on the prolate side of the sphere to remain in tolerance of the
1/4 wave PV parabola. If that is within your tolerance limit of making a
parabola then you can call it a parabola.

Of course the same applies to using RMS or Strehl.  You are the one that
decides the tolerance. That is the answer. 

It would make a good scope but there are some who are stewing in the hell of
perfection and will not accept anything but dead on perfect, and maybe not
even that.

Jerry


-----Original Message-----
From: Dale Eason
 
According to my calculations using OpenFringe the
answer is yes.  The RMS error is 1/21 wave and the
strehl is .92.

Lets see what the Math wizards say. 

However one usually does not get a perfect sphere, so
what ever error it has on the opposite side of
correction will make it worse.  If on the other hand
it has a little correction then that is even better.  


Dale Eason

--- Russell Jocoy <russjocoy@hotmail.com> wrote:

> 
> To all,  Can a 7 inch disk be formed to a sphere and
> polished at f/10 and not be parobolized?..
> And produce correct images to the eyepiece??   There
> are dispute's on this answer..Russ
>
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