Re: DS24 spatial variations

[Stupendous Man <richmond@a188-l009.rit.edu>]

  Me:

>>  a. subtract median darks (which are taken every night)
>>  b. use light box flats (which are taken frequently -- I don't
>>       know if nightly is best, but Andrew's idea of
>>       averaging several sets sounds good to me)
>>  c. apply a correction factor based on (x,y) position on the
>>       chip; this will be derived from grid tests

  Tom:

> So I agree with a. and b. above.
 ...
> What do do after a. and b.?  If I understand the star finding algorithm 
> that comes next, it will be biased if the field is not flat.

  I claim that the bias in the star finding will be small enough
to ignore, but I could be wrong.

> 2) Force the individual image fields to be flat.  Just continuously 
> subtract the background after doing a. and b.  Then find stars and complete 
> the pipeline process.

  Yes, there is very no harm in doing this.  A subtraction is exactly
right.  

  Hey!  I _think_ I'm just about caught up in my courses.  Maybe
I can write a new XVista routine to do this, and insert it (with
option to turn on/off, of course) into the pipeline...

                                 Michael