Re: why so many darks?

[Tom Droege <tdroege@veriomail.com>]

I hope that no one take offense when I say something like "what do you want 
to do it that way for?".  This was a favorite expression of our group at 
the Princeton accelerator.  Everyone felt free to question everyone else's 
way of doing things.  Facts and logic prevailed over degrees and Nobel 
prizes.  Some found it hard to take, but once everyone understood it was 
done without malice we all gained from it.

This is a good attitude when you are doing something out of the beaten 
path.  Just because it is the way "we do things" does not mean it is right 
for the current program.  I will continue to ask that question, and am 
quite willing to learn when I am wrong.  I think we are all teachers 
here.  I for one, am willing to take the time to explain to others the 
things I understand.  I am also quite willing to attempt to think through 
things that I do not understand and to ask for criticism.  I hope the rest 
of you feel the same way.

Michael brings up good points as to why we have a different problem from 
most astronomical cameras.  The temperature control system will do a pretty 
good job when it is allowed time to settle.  About an hour.  The system 
requires cooling water which changes temperature slowly for the TEC 
regulator to work properly.  This just means enough water.

I note that there is a lot of "folk lore" and little thinking in CCD groups 
when discussing dark field and flat field techniques.  One has to work out 
the best scheme to use with the equipment available under its 
operating  conditions.  There will be lots of room for you all to develop 
hardware to optimize these measurements.

We still do not seem to have a "cook book" for processing our data.  I will 
at some point try to revise my last attempt, collecting the various 
suggestions.  I doubt we will get to one standard technique, but it will be 
fun to try.

Tom Droege

At 09:49 PM 12/20/00 -0500, you wrote:

>   You bring up good points.  I was raised on more typical
>astronomical CCD systems, in which
>
>          a) the temperature was fixed by LN2
>          b) the exposures had much lower sky levels
>
>   In those circumstances, the dark noise wasn't completely
>swamped by the sky, and the temperature of the chip was
>pretty well fixed during the night.  Under those circumstances,
>20 darks can make a difference.
>
>   With the Mark IV, however, you are right: more than 5
>probably is overkill.
>
>                                       Michael