Re: [ATM] Acceptable Level of Astigmatism

["David Harbour" <scarab2@cox.net>]

Peter, all:

You will always know the difference between "false astigmatism" and REAL
astigmatism, when seeing an anomolous apparition of the mirror on the test
stand, if you will mount your knife edge and your slit as I recommended only
a few dozen posts ago in my somewhat longish posts about: "On axis Foucault:
Try this Instead". I promise you that this simple way of mounting knife edge
and slit will eliminate doubt as to whether you have "true" astigmatism, or
not. With K.E. and slit mounted as I have described, if there is no "real
astigmatism", there will be no discernable tilt, "monad", in the apparition,
regardless of the focal ratio.

Dave

In the day time the christmas tree ornament test is another back up method
to see how your optics are doing (like "star test" at night, optics
mounted).


----- Original Message ----- 
From: "Peter" <peter@kitgear.com>
To: "Atm" <atm@atmlist.net>; "Atm_Free" <atm_free@yahoogroups.com>
Sent: Wednesday, June 15, 2005 7:35 PM
Subject: [ATM] Acceptable Level of Astigmatism


> Hi,
>
> A fellow ATMer wanted me to ask what level of astigmatism is acceptable
> before it becomes detectable? He's working on a 10" mirror which shows
very
> a slight bit of tilt in the Foucault shadows.
>
> Is there a simple way for an amateur to measure this parameter and
determine
> what is good enough?
>
> Thanks,
>
> Peter
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>


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