Spots

[Tom Droege]

Posted to CCD-world:
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Hi Roy,

Thank you.  This is a low end Grade 4 device.  It also has a bad column.
So I think it is from the low end of the distribution.  Arne Henden now
says such defects are common.  

I think it will not be too hard to flat field them out.  

I am amused by the advice I get from CCD-world.  "Buy only Top Grade Chips
for Astronomy"...   Sounds to me like advice from Marie Antonette.  ;^)

Things are going well, with the usual disasters.  We will soon have a bunch
of 2k cameras in the field.

Tom 

At 09:54 AM 4/21/99 -0700, you wrote:
>Posted to CCD-world:
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>At 01:22 PM 4/20/99 -0500, you wrote:
>>Posted to CCD-world:
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>>The Amateur Sky Survey now has several 2k x 2k CCD cameras running using
>>the CCD442A.  We have bought the Grade 4 (lowest cost) devices.
>>
>>On one of the cameras, I see large round dark spots.  One is a few hundred
>>pixels in diameter.  Others are smaller.  Most of these spots represent
>>lower sensitivity of a few percent.  One has increased sensitivity.  Being
>>the tass list, these have sparked a debate as to their source.  We are
>>running the present CCDs with covers.  (CCDs are now on order without
>>covers.)  In my opinion, the edges of the spots are too sharp to be due to
>>dirt on the cover or in the optics.  The spots are on the only CCD with a
>>bad column, indicating that this is possibly a lower grade overall device.  
>>
>>Can anyone tell me if such spots are common on a CCD?  Flat fielding mostly
>>removes the problem, so this in not all that serious a defect. 
>
>Hi Tom,
>     If these are thinned devices with an anti-reflection coating, these
>spots might be due to a defect in the AR coating. I have a thinned,
>AR-coated device with such an artifact.
>					- Roy Tucker
>
>
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