--- In C14@y..., Scott Evans <sevans@i...> wrote:
Richard,
Your comments are interesting because I had always heard that the
focal
ratio would be the primary factor in determining exposure time
regardless
of focal length. Shouldn't the f/5 fsq be a shorter exposure than
the f/11
c-14?
BTW with the fastar lens installed I have an 735mm focal length 14"
scope. ;-)
Scott
The faster f-ratio equals shorter exposure principle only applies to
extended objects. For stars that are essentially point sources,
exposur time depends on the number of photons collected in a given
time, i.e. the actual aperture, not the aperture ratio.
Hope this helps
Robert Bilsborrow
