Re: ATM CCD's and mirror F/#

[akelly@ghgcorp.com (Albert F. Kelly)]

>>the efficient use of short term photons.....reduced tracking and guiding 
>time
>
>I find it hard to believe that anyone would trade optical quality and 
>image quality for the sake of a few minutes guiding.
>The useable focal area of fast mirrors -f/3 and below is so small and the
need to >magnify the resultant image so great, it would logically say stay
away from fast 
>mirrors! Mass produced f/1.95 mirrors -this i gota see.Wonder how they 
>plan on testing and figuring them?

Ric,
        The CCD chips used today by amateurs are so small that the usable
area of fast systems is usually sufficient to cover the imaging area without
vignetting and noticeable coma.  The logic of fast mirrors, at least down to
f3-to-f3.5, holds up very well for amateur CCD astrophotgraphy.  
        People are not usually "...trading optical quality and image quality
for the sake of a few minutes guiding."  More frequently, people are trying
to get as high a signal-to-noise ratio as they can in as short a period of
time as possible.  In order to retain linear imaging and avoid blooming,
stacking short exposures is the optimum way to reach a really good S/N.

Al Kelly