ATM Alt-alt telescope mount - and image rotation

[tkrajci@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