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Re: Everett and Howell Paper
I think the E&H's longer focal length helps. Even if
both groups have three pixel wide PSFs, TASS's three
pixels see just over 500 square arcseconds of sky while
E&G's three pixels see less then 2 square arcseconds of
sky. Even if the sky is as dark as 20mag/square arcsecond
this has to make a difference
> - is it hardware, specifically full-well capacity or
> effective PSF size? Again, I think "no".
> Both groups use CCD chips with relatively shallow
> full well capacities. The Everett and Howell paper
> implies that they ignored pixels with more than 70,000
> electrons (though they don't state it directly).
> The Mark IV has a similar gain (3 electrons/DN),
> and its full-well capacity is about 80,000 electrons.
> We put all the light from a star into a relatively
> sharp PSF, with a Full-Width-at-Half-Max of about 3 pixels;
> one of the reasons is that our pixels are so big, about 7.5
> arcsec on a side. E&H use a much smaller pixel scale
> (0.43 arcsec/pixel), but focus the light into a FWHM
> of 1.4 arcsec, which works out to about 3 pixels.
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