Re: Time for Software

[<aah@nofs.navy.mil>]

Doing B with a raw 442A is probably not wise; you
would have to construct a special B filter to compensate
for the loss of response on the blue side.  It can be
done, but having such a B camera on the same mount as
the R camera would mean either changing the exposure
times by factors of 6 or so, or else living with the
2-magnitude loss in the limiting magnitude.  Both
are ok, though, when you consider the alternative!
  You can get better blue response either by getting
a thinned backside illuminated device, or by coating
the thick device with something like lumigen.  You
might check with Loral (or whatever they are called
this morning) and see if they can do a coating.  Such
laser dyes absorb the blue photons and reemit them
at a more reasonable wavelength.  You lose a factor
of two from the isotropic reradiation, and some from
the QE hits of both the coating and the CCD, but you
still gain far better blue response at a significant
savings from buying a thinned device.
Arne