Re: [ATM] 20" Fused Silica blank ( a bit long....)

[Jim Burrows <burrjaw@earthlink.net>]

At 2007-06-28 16:03 -0700, William Marriott wrote:

>While this one is
>used as a prime focus astrograph, I believe the design
>could be modified for use as a Ritchey - Chrétien
>scope for visual  use, maybe photography down the
>road.
>
>F6?  F8?  f12?

Whee!  Some other ATM in the universe is thinking 
about an RC cass!  I've been fiddling with an 8" 
f/8 for a "few" years (I won't say how many 
<g>).  It ain't easy, but the math is fun.  The 
surface parameters are primary:  R = 1297.4 mm 
(f/2.6), b = -1.102 (not very hard and I've 
gotten the surface RMS down to 11.2 nm); to 
match, the secondary should be R = -677.9, b = 
-4.8 (currently under construction).  The trouble 
with the secondary figuring is both R and b have 
to get close to those values to get the wavefront RMS down.

Here's a couple of ancient downloads:

         http://home.earthlink.net/~burrjaw/public/aplanat.zip 
(2001-08-27, Win3.2, 15.7 k)  RC cass design,
         http://home.earthlink.net/~burrjaw/public/rc_atm.zip 
(2001-08-27, Win3.2, 7.5 k)  testing

When (if) the wavefront RMS gets down to 40 nm, I'll do a lot of updating.

         -- Jim Burrows
         -- http://home.earthlink.net/~burrjaw
         -- mailto:burrjaw@earthlink.net
         -- Seattle N47.4723 W122.3662 (WGS84)


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