Re: [ATM] Re: Schmidt-Cassegrain

["vladimir sacek" <vlad@copper.net>]

Jean-Guy,


>
> Think i will go for it. I promise you the first pictures,
> but don't hold your breath  ;-)
>

That would sure be interesting, and original as well
(as far as I know). Can't hold breath quite that long,
because wish to be around by the time you have it
finished '). If the speed is important, secondary magnification can go 
somehat lower, as long as the detector can fit in without adding to the 
obstruction.
It would also futher flatten the image surface.

As an example, at the secondary magnification of 1.4,
with identical min secondary size (0.4D), the system would reqiure conics 
K1=-0.708 and K2=-0.172,
with the best image surface curvature ~17m. However,
detector face diameter would have to be less than 50mm.
Similar thing with min secondary size of 0.33D and 1.5 secondary 
magnification.

Secondary can also be smaller. I went with large secondary because I felt 
that room for the detector gets too tight with smaller secondaries. The 
exact relation between secondary magnification "m" and its min diameter "s" 
(in units of D) for flat best field surface
is given by s=(m^2+m-1)/(m+1)(m-1). Then, the max detector diameter (also in 
units of D) is given by
(m+1)sc, with "c" being the relative size of c.obstruction. Note that for 
the Gregorian both "s" and "m" are negative. The deviation from the exact 
flat field relation can be rather substantial before the field gets curved 
enough to require a flattener.

Best reference for figuring out the parameters I know of is Schroeder's 
"Astronomical Optics". Whetever you decide, keep us posted (please?)...

Vlad 


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