Re: [APML]: Image Registration

[Chuck Vaughn <aa6g@aa6g.org>]

The Astro-Photography Mailing List
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Michael,

Thanks for the suggestions. My experience has been somewhat different though.
I've had minimal trouble aligning the refractor photos and major trouble
aligning Newtonian with coma corrector photos. And this is after using the
PS Layers:Distort. The major trouble has been with negatives where the
center of the field is not the same. This is essentially not a problem with
color negatives taken in succession.

I don't know exactly what the specs for the Lumicon coma corrector are but
I don't believe it is a field flattener, is it? My friend's corrector is a
custom designed two element air spaced coma corrector/field flattener that
exactly matches his 8"-f/6 Newtonian. Somehow this corrector is causing a
toroidal distortion as I described before....some stars need to be moved in...
some out. And it's a lot...as much as 3 or 4 pixels on a 2700 dpi scan! One
of the things he's going to do is go back to the designer and ask about
distortion introduced by this design.

>From the messages I've read so far I don't think anyone has run into quite this
problem before. I think I'll go ahead and make the two worst images available
to the group and see if someone scan figure out something I have not. At
a minimum it will make the problem more obvious.

Chuck <aa6g@aa6g.org>

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>      I have not done tricolor for some years now, but know that others
> sometimes have to use Photoshop in order to register difficult photos.  As I
> understand from James Foster, he uses the Layers -- Transform -- Distort
> command.  This allows for better alignment because of the problems of
> chromatic aberration, field curvature and the many problems Jerry talked
> about.  Also I think you will have far less trouble if you use a reflector
> instead of your refractor for tricolor.  I initially tried tricolor with my
> 5" inch refractor, but gave up on the method because of the chromatic
> aberration and registration problems.  There are ways around this  (Distort
> and blue star treatment), but they are difficult to do and as long as PPF is
> around, I do not think they are worth the effort. An exception would be for
> those unusual conditions where color film does not work very well (e.g.
> S-147).
>      I must be lucky because I have had no image registration problems with
> Picture Window when stacking my color negatives.  If you need help with your
> tricolor work, I suggest you contact James Foster or Bill Fletcher.  They
> have known about this problem for years and and should know how to deal with
> it.
> 
>                              Michael Stecker