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Re: Darks and Flats



Tom wrote:
>The weather is bad, so I had Dan modify the flat field box and I am running 
>darks and flats.

  This is with both cameras, or just one?
  Regarding light sources:  the primary reason for using
tungsten/quartz lamps is that they have a continuous black-body
spectrum, as opposed to Xenon flash or white LED or fluorescent lamps.
What you want is *some* output at every wavelength passed by the
filter.  The secondary consideration is a matching of the lamp
color to the color of the night sky.  There is no tungsten lamp
that is blue enough, but in general at V & I the output is ok,
even at reduced voltage settings.  It is at the blue end (U and B)
where you have problems, not only due to the lamp but also due to
the falling CCD response.  What we do there is to use a color
filter in front of the lamp to artificially make a 'blue' bulb
when we want the closest match.  The other approach is what I mentioned
before:  high output flat from the lightbox, gradient and color
correction from smoothed night sky frames.  Don't worry about the
secondary corrections until you get the first order correction done!
Arne