[ATM] Higher order Null Lens for RC primary

[Gert Gottschalk <drgert1@yahoo.com>]

Hi,

Is there a suggestion for a higher order Null-lens (is
this then still called 'Dall'??) for mirrors faster
than F3 or strong correction?

I made a 10" RC primary (F2.6, SC=-1.17) and tested it
with zone tests, only. The correction is OK but with
the steep curves it is impossible to judge if the
surface is free of zones.

There is a nice analysis for the use of Dall lenses
for paraboloids at : 
http://www.atm-workshop.com/dall-setup.html

When applied to the F2.6 primary however residual
higher order spherical aberration is no longer
negligible. (about 0.6waves P-V)

My question. Has someone come up with a design for a
Null-test system (2 lenses) that can be based on
catalog lenses and is robust to tolerances for ATM use
(kitchen table proof) ??

Thanks,

Gert

drgert1@yahoo.com


		
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