To: atm{at}shore.net, atm_free{at}yahoogroups.com, scope-drive{at}yahoogroups.com
From: tkrajci{at}san.osd.mil
Reply-To: tkrajci{at}san.osd.mil


I'm doing some math analysis of image rotation of various types of
telescope mounts.  One example is at:
http://overton.tamu.edu/aset/krajci/scope-design.htm
where I discuss image rotation in the alt-az mount design.

As many of us know, the alt-az design can't access the zenith.

But the alt-alt design can.  (Think of an equatorial mount, but lower the
polar axis so that it's horizontal...but still pointing to the north.) The
alt-alt can't access the extreme southern and northern horizons...but
that's seldom a problem for astronomers...and often far better than losing
the zenith, which is the problem for alt-az.

I have looked through this book:
http://www.willbell.com/tm/telecont.htm
and it provides equations for alt-az telescope motion and image rotation.
(It does not provide the same equations for alt-alt designs). Unfortunately
my trig. skills are not good enough for me to derive equations to determine
alt-alt telescope motion and image rotation.  (Yes, I can tell by looking
at the alt-alt design that field rotation will be worse when imaging near
the low southern and northern horizons, but I need more precise
descriptions.)

Can anyone help me?

Based on field rotation of the alt-alt design...I may consider a future
telescope with such a mount.  It might allow CCD imaging without the need
for a de-rotator at the focal plane if the alt-alt design keeps image
rotation low enough.

Thanks in advance,
Tom Krajci
Tashkent, Uzbekistan

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