Sloping bias frames

[Paddy Oates]

Roger, Huw and others,
	Thanks for the rapid response. Good to have plenty of knowledgeable
folk to the West of us who get up after our problems have made themselves 
known!!!
	The chip is in a camera head on the Island so I cant do anything with it 
myself. I have kust confirmed it is to be sent back to RGO next week. The 
trouble is it has been operating okay since I took it out at the beginning of 
May this year so its difficult to see that for example a clock phase problem 
should suddenly occur.  (from Huw)
	Roger thanks for your ideas, Heres a table of how I think things 
look, the table shows the presence or absence of the gradient for the 
differing coonditions-

			V-Clock direction
		FORWARD			REVERSE
Int. Time.	---------------------------------
0		yes			Yes
1		NO 			Yes
10		NO 			NO (I think!)

The exposures were made on the spectrograph with the dome lights ON.
>From the overscan on second of the binned images on my Web page , 1 sec exp 
lights on, there is no evidence of light in the overscan pixels and so no light 
is getting on the CCD, The back clocking scheme anyway rules out smearing due to 
light leakage.The serial reg. is scanned during integration. This is a loral 3 
edge buttable with 1 register and 2 ouputs - both outputs show the same effect. 
It has only recently (last 5-6 days) occured. It wasnt there when I installed 
the head in May.
	From the above it appears that the chip needs some light on it before 
behaving correctly, The reversed clocked zero sec exposure seems to rule out the 
electronics... 
	The observers are happy to live with this for the next night or two - it 
only apparently affects bias frames, NOT the science data... though I am still 
wary about all this. It looks as if we may have caught some subtle on-chip or 
register effect not seen before...

If I find the culprit next week will post the good news

Cheers
PAddy
		

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