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Re: [ATM] turned edge vs over correction

Hello All,

I like this topic because I have problems with both overcorrection and
turned edge very often,
mainly with turned edge. Could you recommend me what to do?
1) How prevent turned edge during polishing?
2) How correct turned edge after polishing if it come up?

I think that ATM recommends adding TOT between MOT during polishing.
But my experience is just opposite. It takes more glass from edge and makes
mirror overcorrected and turned edge...?

Thanks for help,

Libor


----- Original Message -----
From: "James Mulherin" <jcmulherin@opticalmechanics.com>
To: "'Wayne Hilliard'" <woodycxd@adelphia.net>; <atm@atmlist.net>
Sent: Tuesday, November 01, 2005 2:26 PM
Subject: Re: [ATM] turned edge vs over correction


> 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
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
>
> _______________________________________________
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