[ATM] Luri-Houghton prescriptions.

["Bob May" <bobmay@nethere.com>]

I've been playing with the Lurie-Houghton prescription on the two
lenses and seem to find that the equal radius pairs of curves
doesn't seem to do the best job.  The equal radius curves seem to
do some inverse coma along with more astigmatism than doing
different radius curves for each surface.
What I've come up with is the following set of curves for the
typically specified lens set:
Object
0 12.5
Refraction
BK7 0 -96.3
Refraction
Air -0.81 275.9
Refraction
BK7 -0.96 96.3
Refraction
Air 1.457 -275.9
Mirror
-61. 119 0 13
FocalPlane
-1.69403
WAVELENGTH
0.643 0.54 0.486
while a much better result is:
Object
0 12.5
Refraction
BK7 0 -107.09
Refraction
Air -0.745 201.726
Refraction
BK7 -0.78739 94.3063
Refraction
Air -1.27146 -271.735
Mirror
-61 119 0 13
FocalPlane
-1.57512
WAVELENGTH
0.486 0.54 0.582
ANGLE
0 0.0066 0.01
FOV
0.0005
the format is in Dave Rowe's TRACE program where the first number
is the distance and the second is the ROC of the surface.
The first data set gives a spot size of 0.00024" in diameter
while the second gives a spot size of 0.00012" in diameter.  The
images of the spots on the first show that the off-axis spot has
a bit of inverse coma and the size of the spot is about twice the
size of the second set of spot diagrams where the way off-axis
spot shows a nice oval which indicates only astigmatism.
Any comments?  I've got a guy that is about to build the scope
and I'd want to make sure that he builds the best possible.
Bob May
bobmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
Addresses have been munged up to keep spammers from bothering me.
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Thank you for your understanding!

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