Spots

[Tom Droege]

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. 

Tom Droege
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