Re: [ATM] turned edge vs over correction

["James Mulherin" <jcmulherin@opticalmechanics.com>]

Wayne:

In my opinion, yes. Let's imagine your outer 1/2" is over-corrected by 1/4
wave. No problem, your mirror is still diffraction limited. If your outer
1/2" is over-corrected by 1/2 wave your images will still be good but they
will be a bit softer and you lose some contrast. However, all of the star's
light still goes into image formation. It's not perfect but it's still quite
good. 

A turned edge on the other hand is so steep that it no longer contributes
light to the focused star image. In stead, some of the light goes to making
your star images hairy (the hair is outside of the normal image circle) and
the rest is spread throughout the rest of the field of view, reducing
contrast.

There may be some argument as to magnitude. In other words, where's the
transition between over-corrected and turned down? This is a tough question
to answer without empirical data and on the sky testing. On the sky you can
usually recognize a turned edge immediately. It takes some skill in
interpreting the star test to diagnose an over-corrected edge.

James

James Mulherin
Optical Mechanics, Inc.
jcmulherin@opticalmechanics.com
www.opticalmechanics.com
Tel: (319) 351-3960
Fax: (319) 351-3943

> -----Original Message-----
> From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf
> Of Wayne Hilliard
> Sent: Tuesday, November 01, 2005 5:20 AM
> To: atm@atmlist.net
> Subject: [ATM] turned edge vs over correction
> 
> Is there a difference between a overcorrected 100 percent zone and a
> turned
> edge?
> 
> 
> Thanks
> 
> Wayne Hilliard
> 
> --
> Wayne Hilliard         "If computers are making the world a global
> village,
> KA1CXD FN32             and I can't figure out how to use one, does that
> woodycxd@adelphia.net   make me the global village idiot ?"
>                                                      Shoe
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