Re: [ATM] 7 inch sphereical mirror

["David Harbour" <stainless_steel@suddenlink.net>]

Amen to that, Jerry-

R-101

----- Original Message ----- 
From: "Jerry" <wa4guu@verizon.net>
To: "'ATM list'" <atm@atmlist.net>
Sent: Saturday, April 12, 2008 9:51 AM
Subject: Re: [ATM] 7 inch sphereical mirror


> 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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