Re: [ATM] Front aperature size on 20" RC

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

Hi William,

Wednesday, August 29, 2007, 12:26:54 AM, you wrote:

WM> With a 20" f4.25 primary, and f8 overall, I am making
WM> an assumption that the front aperature (secondary
WM> ring) inside diameter could be 22 inches.

People may jump in with all sorts of rules of thumb Bill, but without
knowing the length of the tube and your field angle nobody can answer
your question.

Optically, you should allow an absolute minimum radius increase of the
secondary ring of : the tube length times the sin of half the field of
view. Thermally, you may want more. Baffling is another question
entirely, which MODAS does a fairly good job of working out for you.

-- 

Best regards,
  Richard in the UK

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