Re: CCD Window

[Arne Henden <aah@nofs.navy.mil>]

As Michael R. mentioned, it is unlikely that the windows are
causing the noise floor.  They add increased scattered light,
loss of light, ghosting, possible limit of spectral response,
etc. which is why most pro cameras remove any cover plate.
I agree with his assessment of the noise floor, and his
suggestion to leave the covers on.  If you had a really leak-proof
camera head, then you might consider removing them.
Arne

Thomas Droege wrote:
> Reading the CCD-World list I realize that I have probably bought windows
> without anti-reflection coatings.  A comment by a manufacturer on the list
> says that if chips are ordered with glued on windows they get glass with
> anti-reflection coatings, but if taped on windows are ordered they get
> plain glass.  So there is a good chance that some or all my chips have
> plain glass windows.
> 
> I am wondering if this could cause our noise floor?
> 
> If images are taken in the same position, then the reflections would be in
> the same places.  So while they would add to the noise, they might be
> consistent and would be calibrated out by the pipeline.  However, moving
> around in position there would be no way to calibrate reflections.  What do
> you all think?
> 
> I could easily remove the cover glass.  This at least removes two surfaces.
> Now that the cameras are working pretty reliably, I would not mind removing
> the covers.  However, one trades dust on the window which is out of focus
> for dust on the surface of the CCD which covers specific pixels and
> probably moves around a little.  Anyone had experience with this that can
> make a recommendation as to the trade off?
> 
> Tom Droege
> 
> 
> Tom  Droege Jennifer Malpass
> tdroege2@earthlink.net
> 
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