Re: [ATM] Gimbaled Secondary mirror

[Stan Truitt <s.truitt@verizon.net>]

>Just a small note. Tilting or displacing a secondary introduces coma
>as well as the desired shift of the image. Turns out that by
>simultaneously tilting and displacing with a specific ratio (meaning
>pivoting the secondary around a specific point along the optical axis)
>you can mimimize the coma error.

Bill Wetherell published that same information, along with a broader 
treatment of Cassegrain type considerations, in the March 1972 SPIE 
Proceedings Volume 28 (Instrumentation in Astronomy) pp 45 through 
79.  The filet cuts are pages 69 through 71, from which a tip-tilt 
secondary scanning mechanism was designed for an adaptive optics 
corrected 1.6 meter Cass satellite tracker at Haleakala, Maui.

Dan Schulte's paper on offset guiding follows immediately after Wetherell's.

Hope this helps,

Stan Truitt
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