RE: ATM 8in Mirror Specs

[Chuck Dethloff <telmor@teleport.com>]

Over the years I have used scopes ranging from f/4 to f/15.
I have found that f/4's are perfectly capable of being well collimated if
you use care when collimating. And I don't do anything differently
collimating an f/4 than I would an f/8, I try to nail either one dead on.

And they certainly can provide excellent planetary images if they have
good optics. My wife's 16" F/4 (about 1/10th wave) has shown O'Meara
(also myself on a couple occasions) spokes in Saturn's rings and many
other _very_ subtle planetary details over the years. I have also gotten
excellent views through a friends 8" and 12.5" f/4 on the
planets. 

So, while it is true that they should not be considered an optimum
planetary scope, they also should not be thought of as not being capable
of delivering high quality on axis images. Those that have the opinion
that they are poor planetary scopes probably have not had access to well
collimated good quality fast optics. ;-)

You can do an f/4 and still keep the central obstruction down to around
20 percent. 1/4 wave is not good enough quality though for quality
planetary viewing, if you opt for a faster scope you should look for one
around 1/10th wave. 

Chuck Dethloff