Re: [ATM] Look for meniscus parameters of Meade LX200 7"Maksutov-Cassegrain?

["vladimir sacek" <vla@toast.net>]

Since you have the instrument at hand, you can get 
much closer actual parameters than Gene Cross' 
pre-production estimate. It would suffice to determine 
primary (center) and back of the corrector separation 
from the end of the baffle tube (it can be done safely 
with proper care taken). Relative front meniscus surface 
position can also be closely determined by measurement. 
This would closely determine position of all four optical 
surfaces relative to each other. 

Curvature of the front meniscus should be easy to determine 
with a light source at the center of curvature. Back surface 
curvature may be concentric, or "achromatised", in which 
case it relates to the front surface radius as 
R2=(1.76R1+t)/1.76. 
Since the secondary is an aluminized spot on the rear surface, 
the rear surface curvature can also be obtained by measuring 
it via c.o.c. reflection.

With positions and radii for all elements approximated, it is 
possible to approximate system's spherical aberration with 
the primary spherical, and then aspherize it as needed to have 
the aberration cancelled. This would round up a system that 
should be close to the actual design performance-wise.

Vlad 
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