Re: [ATM] Gimbaled Secondary mirror

[Mauritz Andersson <mauritz.andersson@gmail.com>]

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. This is discussed in the article by
Wetherell and Rimmer, Applied Optics vol 11 page 2817-2832, 1973.
Distance of this neutral point from secondary surface is according to
their analysis
 L=R (1+m) / [ (m+1) - (k-1)(m-1) ]
where R is the radius of curvature of secondary, m is the secondary
magnification and k is the conic constant of the secondary.
Mauritz Andersson
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