Re: ATM Cassegrain formulae

[Andy Saulietis <iss@pvtnetworks.net>]

Thomas Janstrom, re 42" Nasmyth Cass:

>BTW I would appreaciate any advise the group has to offer on this matter, on
>any part of the project.

Having built & used a 16" Nasmyth Cass, these
are some suggestions & comments:

- the reverted image (3 reflections) can
  be a nuisance at times. One way to fix it would be to
  build a roof mirror but expensive & adds a 4th reflection.

- Highly recommend enhanced coatings on at least the sec
  & tert mirrors, standard coatings (90%) lose a lot
  of light with 3 reflections

- clean mirrors often, lots of scatter with 3 reflections

- design such that system is fully baffled with somewhat
  oversized secondary, the increased contrast & usability
  in daylight is worth the small amount of light loss.
  In this size, going for a small sec to minimize
  diffraction effects is not worth it a the scope will
  be seeing limited 99% of the time



 
Andy Saulietis
ISS Enterprises
39 Silver Fox Trail
Mayhill NM 88339
505-687-3067 voice
505-687-3021 fax, call voice or e-mail to set up
e-mail: iss@pvtnetworks.net