Re: [ATM] 16" RCC primary

[Richard <cnc@cncservo.co.uk>]

Hi Attila,

Saturday, January 21, 2006, 4:59:46 PM, you wrote:


AS>       I started a RCC project some month ago.The system includes a 16"
AS>       f/4
AS>       primary, which is right now at the state of paraboloid. But this
AS>       system needs an hyperboloid primary.

It is much harder to figure the convex hyperboloid secondary
than the primary, so the best course is to make the secondary
first and get as close as you can to the desired K. You then
recalculate the required K for the primary based on the known
parameters of the secondary.

There is an excellent web page here on testing the secondary :

http://www.users.bigpond.com/PJIFL/page13.html

For the primary, some form of Null test would be best, but as
you are lucky enough to have such a lovely big flat,
autocollimation would be your best way to figure the primary to
match the secondary.

Depending on your final F/ number, a 0.7" diameter field should
easily be diffraction limited from a RC, and definitely coma
free. Well worth getting the hyperboloid constants correct and
you will have an excellent telescope, for visual or photographic
use.

F/4 sounds quite slow for an RC primary. Is that to keep the
secondary diameter small?. Want to share your
prescription?

-- 

Best regards,
  Richard in the UK

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