Re: [APML]: Astrophotography on southern hemisphere

["Michael Stecker" <mstecker@earthlink.net>]

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-----Original Message-----
From: Chuck Vaughn <aa6g@aa6g.org>
To: astro-photo@nightsky.com <astro-photo@nightsky.com>
Date: Saturday, August 29, 1998 7:30 AM
Subject: Re: [APML]: Astrophotography on southern hemisphere


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Chuck:
     In order to get rid of the halo problem, you only have to do two
things.  First, do not use a refractor for tricolor work.  Both Bill
Fletcher and I have learned this several years ago.  You will never see a
tricolor photo taken with a refractor by Bill.  His standards are too high.
His excellent tricolor work is all done with reflectors and he does not have
a halo or "color" problem.  Secondly, halos can be seen with over exposure
resulting in excessive halation.  This is especially evident (red halos)
when using PPF color film with high quality refractors.

      If you or others on the list want a Photoshop method that will rid
your photos of halos (blue) then please read James Foster's technique on his
web page.  I use a modification of this technique which I call " the blue
star treatment".  This will remove all the blue halos through a selection
and "similar" technique.  The halos of all stars can then be simultaneously
shrunk (JF) or neutralized (MS).  You will then have no halos in your image.
Of course this has not solved the basic problem that the refractor is not an
apochromat and is not accurately focusing all colors to the same point.  If
you want this, then use a reflector.

                        Michael Stecker