Re: Last Night's Run

[Tom Droege <tdroege@veriomail.com>]

I know Arne wants overscan pixels.  They are there, just not as many as one 
could get by reprogramming the PROMS.  Someone could look at the last 
column vs temperature on the 18 disks when you get them.  It is on my list, 
just that it is not ahead of finding things like the problem of the other 
night where it started taking garbage at 2 AM.

My present read out scheme is just for my data collection at the equator 
with TOM.  This gets a lot of nice overlapping data with uniform times and 
bias accumulations.  The rest of you are free to use a better program or a 
different sequence to take better data.  If fact, I am hoping that someone 
will do it right.

Tom Droege

At 12:09 PM 5/14/01 -0700, you wrote:
>I will say, just one more time, that the bias drift can
>be removed easily if you implement overscan.
>  Tom's scheme on image collection (unless he has changed
>it recently) is to read out the previous frame, then
>expose, then read out the new frame.  The two reads
>make it so that each pixel has the same amount of dark
>current + a shuttered exposure.  However, what is variable
>is the time from the previous read until the shutter opens
>for the current read, since you might move the telescope,
>store the last frame, etc.  So the amount of dark current
>is not always obvious nor constant, even if the CCD
>temperature is accurately controlled.
>   A single bias frame is not the way to go, since the
>noise in that single frame will propogate into all data
>frames.  You should create a 'master' bias by averaging
>many such frames.  Doing this at twilight is not the
>right way to go either, since there are light leaks
>in the system.
>Arne