Re: Curious Result

[Tom Droege <tdroege2@earthlink.net>]

I woke up (5:30 AM) thinking about this.  I realize that the right side it 
scanned first, and the left side is scanned last.  This indicates a clock 
problem.  Sigh!

Looking at the log book, I did an experiment to optimize the clock voltages 
on 000928.  Looks like I don't have them quite right.  This would cause a 
change in the saturation level from top to bottom of the image.  Possibly 
also a top to bottom gain change.  The clock voltage to worry about is VVH.

There may not be an optimum that will give equal gain top to bottom.  This 
could be a charge transfer efficiency problem that we will just have to 
live with.

Those of you worrying about this sort of thing (Andrew, Michael) might 
consider whether one can apply a top to bottom gain fit that would make a 
correction.

Meanwhile, I will take some data with different settings for VVH and see if 
I can make an improvement.

I propose to take a series of sets of 10 images tracking various star 
fields with different values for VVH.  I will then reduce the data and make 
mag sigma vs mag plots for each set.  We shall see.

Tom Droege

At 11:50 PM 3/19/03 +0000, you wrote:
>I have attached the file "tilt.png".  This is the pipeline output 
>processing 4 x 4 degree squares taken on even 4 degree boundaries.  The 
>telescope is scanning on centers from -4 to +16 in declination covering -6 
>to +18 degrees.  There was lots of moon and some clouds, so many of the 
>squares were rejected.
>
>You will notice a tilt in the data squares.  It is about 0.1 degree per 
>box.  This means that I am off 1/40th of a radian or about 1.5 
>degrees.  This is not unexpected.  Now that I have Michael's nice 
>make_list.out data I can get it straightened in a couple of observing sessions.
>
>What is curious, is that there seem to be more stars found on the right 
>(Higher RA) side of the image than on the left side.
>
>Any one have any ideas as to why??
>
>Tom Droege
>