Re: final section of TN 0085 is in place

[Tom Droege <tdroege2@earthlink.net>]

First, thank you Michael for this nice TN.  As already noted, the exposure 
length is 100 seconds.  With a read out time of 46 seconds, I get an image 
about every 150 seconds, so there is little wasted time.

Looking at a possible problem with the I images.

There is a bad "column" on the chip.  This was noted by Andrew 
Bennett.  This causes stars that traverse this column to dip in value on 
the frame where the cross.  This gives plots for constant stars that dip as 
they pass over this column.  In fact, they usually have a low point then go 
to zero for several frame times, then pick up another low point rising off 
the defect.

This column should be patched out by the process that generates the 
flats.  It is not for my runs where I use a light box flat set.  This is 
the same flat set that I passed out with DS20.

If you look at the images of DS20, you should see this bad column.  It 
starts as a little black streak with the "head" at x = 1959, y = 461 as 
viewed with DS9.  The pipeline only patches out 62 pixels around this 
area.  This is because of the type of defect.  The defect does not "lose" 
photons, it just smears them out down the column.  So if you look for low 
patches with a dome or light box flat, you don't see any.  (Except for the 
one small black spot at 1959,461.)

I remember setting out to correct this some time ago and I asked Michael 
for the definition of a row and column.  I did not understand the answer so 
I did nothing.  But what I see does not make sense.

1) The patch table does not seem to match where the defect is seen with DS9 
which sees it at x = 1959, y = 461

master_flat_I.msk

0	6072	0	2023	0	2
1899	62	450	470	1948	1953

The I.msk seems to have values for entry 1899 that are close to the defect, 
but they do not match the spot I see with DS9.

2)  The mask does not realize that the defect extends down the whole column.

I will run some more data with a properly patched table if I can figure out 
how to do it.  Michael, possibly you can look at that spot and tell me what 
the table entries really should be.

3)  I think there is one more problem in that the overscan and dark columns 
are not correctly selected.  Looking with something like DS9 will show 
where they really are.

Tom Droege