Re: [APML]: 500-700 mm range

[Michael Stecker <mstecker@earthlink.net>]

Hello Mark Kaye:
     I read with interest your comments on the Cervalo telescopes.  I am
not familiar with them, could you elaborate?  What aperture, f-number
and optical design does he use?  
     I use both the 5-inch and 6-inch Astrophysics EDF refractors and
love them.  I highly recommend these scopes for Astrophotography.  I
also have a Takahashi Epsilon 200 (8-inch aperture at f/4).  This scope
has a flexure problem with exposures longer than 45 minutes.  However,
at f/4 this is not a problem with the newer color films which require
shorter exposure times.  Tech pan with filters however, is a problem
with this scope.  Takahashi have improved their Epsilon series since I
got mine and I understand that the 6-inch model is also excellent and
does not have a flexure problem.  The photos I get with my Epsilon 200
(and 10-inch f/4.5 Newtonian) are definitely superior to my two
Astrophysics scopes.  The images are very sharp, contrasty and have
better resolution.  There is no substitute for aperture as long as you
have fine optics. The only other problem (besides weight) with the
Takahashi is that it does have mild uneven illumination (vignetting)
because of a relatively small secondary mirror.  Is this a problem with
the Cervalo scopes?  I rarely use the Takahashi anymore because the AP
refractors are so easy to use, have excellent optics and do not vignette
(except for the corners).

                           Michael Stecker