Re: [ATM] Luri-Houghton prescriptions.

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

The curve changes are not all that great and, due to the basic
curves, chromatic aberration really isn't that significant.  The
thing that I'm seeing is that the off-axis spot image is a lot
smaller with the change in curvature.
I've found that with this set of numbers for a 12.5" F4.6 scope
to be:
Material  distance  ROC
BK7         0          -107
Air          -0.74      201
BK7       -0.779     94
Air          -1.34     -271.5
Mirror
distance   ROC  SC      diameter
-61          119    -0.01    13
FocalPlane
-1.55163
These numbers give an overall spot size of less than 1/2 of what
the equal curve prescription.     It is pretty much within 1% of
long numbers for each of the values.  Also note that the lenses
are bent from what the equal curve prescription has.  I suspect
that the bending of the lenses is wrong.  With the equal curve
prescription that I've got, the biggest aberration appears to be
negative coma followed closely by astigmatism and both of them
are of significant size.  I can accept a fair bit of astigmatism
as this is apparently a result of the design but having any coma
appears to be not right.
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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