Re: [APML] The perfect astrophoto book (Was: North American Nebula (or dodging aurora))

["westergren" <westergren@netzero.net>]

Robert,
A subject that hasn't been discussed much is Atmospheric Differential
Refraction (ADR).  It shows up as elongated stars that seem to rotate around
the guide star ( more elongation the further from the GS) and is often
confused with and called field rotation.

I ran headlong into ADR with some of my off-axis guided with my 4'f5 scope
with long film exposures of moderate altitude subjects.  I studied the
causes of ADR and now have a way to control it.  I would be glad to share
that information with you for your book(s).  It applies to widefield as well
as long scope film astrophotography.  It's not a problem (yet) for CCD
images because of their narrower field of view and shorter exposures.

I believe that ADR is often called field rotation because Covington's book
describes field rotation very well, with excellent examples.  ADR looks
exactly like field rotation, but is caused by completely different factors.
Since ADR has not been discussed much, many astrophotographers are not aware
of it.

Don


> > Robert Reeves wrote:
> So to answere your question, yes, I am planning another book, but these
> things take time.  After all, I have to earn a living in the meanwhile
<G>.
> It took four years to get Wide-Field Astrophotography into print.  I
> immagine it will be a few more years before a companion or follow-on
version
> is complete.
>
> At this point, perhaps I should ask the collective conciousness of the
APML
> list what topics would you like to see addressed if there was a new book
> about "everything except wide-field astrophotography".  Such perspectives
> from the list members would be valuable in planning such a project.
>
> Robert Reeves



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