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Re: Flat fields are not the problem

Michael Gutzwiller wrote:

> If the lens droops from gravity you would expect the deviation to be in
> the worst direction for the Mark III, straight down in declination.
> Also since the lenses are bolted and glued into position, a droop would
> seem inevitable to me.
> Mike G.


Good theory,  Seems that you could test your idea.  Move the focus ring
on the lens a little each way.  If the CCD is not normal to the optical
axis you should see the point of best focus move in dec.  Best focus 
would place the minimum sized PSF at dead center.  

If the varying PSF is due to smear caused by diferential drift scan
with dec then you should be ablie to move the best PSF by adjusting the
VCO setting.

It just occured to me that the optimal VCO setting is not the one the
cooresponds to 0 deg but 0.75 deg (plus and minus)  This should provide
the best overall.  I don't know if the VCO setting acurate enough so
it makes adiference but still the lens droop theory is testable.


--Chris Albertson

  chris@topdog.logicon.com                Voice:  818-351-0089  X127
  Logicon RDA, Pasadena California          Fax:  818-351-0699