Spots

[Roy Tucker]

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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