Re: Curious Pattern

[hjohnson@pluto.njcc.com (Herbert R Johnson)]

On Fri, 11 Aug 2000 18:03:55 -0500, Tom Droege <tdroege@veriomail.com> wrote:
*>I have been testing cameras.  I have come across one with a curious 
*>sensitivity pattern. Camera N 11.  The background on this camera  looks 
*>almost like a figure 8.  The lines of the 8 are increased in 
*>sensitivity.
*>
*>This just to hint at what flat fielding might entail.  The un-corrected 
*>screen looks like a big fat beetle with pinchers up to the left and a funny 
*>eye to the right....

The flat field image shows the products of the CCD's sensitivity, dust on the
chip, grease or glue on the CCD cover glass, distortions in the optics (and
dust and junk), and any characteristics of whatever the illuminating source
is. A symmetric pattern suggests a lens phenomena, as the lens is symmetric.
If you could rotate the lens see if the pattern "follows" such a rotation.
If the problem is external light sources, the pattern should shift as the
camera moves, or of course vary over time.

Herb JOhnson


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