RE: ATM 8" F/7 Astigmatism

["CSC" <optic@gwi.net>]

Heart rending....er warming or something.

Yes, I have the slant-6 mind syndrome.

I look for a change of shape induced by rotating the tested mirror to detect
irregularity.  All other errors induced by eye defect or test alignment are
somewhat cancelled, non?

What? Use the brain as a processor?

ATM= Anachronistic Telescope Makers

A secret, esoteric ATM society.

Who would know?





-----Original Message-----
From: Richard Schwartz [mailto:richas@earthlink.net]
Sent: Saturday, October 18, 2003 3:05 PM
To: CSC
Subject: Re: ATM 8" F/7 Astigmatism


What brilliant source told you about the eyepiece method of judging
astigmatism?   That test is an artifact of the age of Adolf Hitler!   I
guess you know it requires a pinhole; it won't work with a slit or a
slitless tester.   Also, I guess you know that astig in they eyepiece== or
even in your eye== can throw you off.

But there is a very simple test for astig that does work with a slit.   I'm
sure that my mention of this is enough for it to be immediately obvious to
you.

The attached file is a popular song from the age of eyepiece testing for
astigmatism.  That age is now past.

. . . Richard
from the Republik of Schwarzeneggar
Heil Hindle!

----- Original Message -----
From: "CSC" <optic@gwi.net>
To: "Atm" <atm@shore.net>
Sent: Friday, October 17, 2003 4:10 AM
Subject: RE: ATM 8" F/7 Astigmatism


>
> This is a case where you need more kinds of tests to really confirm what
> you're doing, but I believe your results do show astigmatism. replace your
> slit with a pinhole (fairly small) and observe the image with an eyepiece.
> It should be oblong and will rotate when you rotate the mirror.  .036 is
> enough to ruin an image, but not too much to polish out. It could take a
few
> hours.
>
> Why not try a couple polishing spells to shorten the long diameter's
radius?
> If done slowly, you will see the .036 drop.  When you can't tell anymore
> with certainty, do some long spells of normal polishing, some with MOT,
some
> with TOT, and blend it all out.
>
>
> Colin
>
>
> -----Original Message-----
> From: owner-atm@shore.net [mailto:owner-atm@shore.net]On Behalf Of
> david.a.stevens@gm.com
> Sent: Thursday, October 16, 2003 8:24 PM
> To: atm@shore.net
> Subject: ATM 8" F/7 Astigmatism
>
>
>
>
> This is the latest for my astigmatic mirror. I have measured across 1
> diameter of my mirror ( diameter 1-3 ) and I take an arbitrary measurement
> at about the 70% zone. I rotate the mirror 90 deg. and take another
> measurement  on the 70% zone  ( diameter 2- 4 ). Dia. 1-3 is closer by
.036
> and the shadow is oblate sphere ( high edge,high center). Dia. 2-4 is
still
> oblate but closer to a sphere.
>
> What to do???
>
> A.) Do I keep polishing towards a sphere and hope the astig. will go away
> ??
>
>
> B.)  Do I polish along the short diameter ( 1-3) TOT for 15 or 20 min.
with
> no tool rotation??
>
>
> Any help is very much appreciated,
>
> Dave
>
>
>
>
>
>