RE: Focus indication

[<aah@nofs.navy.mil>]

Tom, you have now presented a design requirement instead
of just a blanket 'focus indication.'  This is much easier
to program towards.  Simple focus is better to perform and
check with a manual interactive operation such as the focus
plate.  Testing for nightly problems is a different beast
and will require a different approach, which is why I am
glad you have presented the exact problem you want solved.
  Automatic fwhm calculation is not trivial, as I have
already mentioned.  Once you want to set limits, then it
depends greatly on the field that is being imaged.  For
example, when you are in the Milky Way, there will be
many more stars and lots of blending.  What kind of fwhm
is going to be generated as compared to a high galactic
latitude field?  Do you want to be woken up every time
a cloud passes over, or every time you get close to the moon
or approach the Milky Way plane?  There will be things
that are easy to check, such as clouds or lights, where
you will have few stars or have a high background or high
standard deviation.  Other things, like sticking shutters
or failing drives, may be a lot harder and I am not sure
fwhm is the answer.
  Your concept of real-time data quality analysis is the
right way to go, but I think it will be a blend of several
different tests, which may or may not include fwhm.  So
my basic question is how much effort to put into automatic
generation of this number.  I'd like to see some discussion
on the list about how people think each of these problems
could best be detected.
  Sorry to ramble on so.  I keep forgetting my resolution
to back off and let others get a few words in edgewise.
I'll stay quiet for a while!
Arne