Images by Tom DROEGE.
Background removed for all images.
X scale is pixel.
Y scale is ADU.
Fig 1. Photometric Profile around non saturated star
Centered on green line
From top to bottom, colors are:
Red, Yellow, Green, Cyan, Blue, Magenta, Black.
FWHM is 1.8 pixel.
A faint ring, centered on the brightest star is visible.
Note the dissymmetry of the PSF (left side is sharper).
Fig 2. Photometric Profil around saturated star
Centered on green line
From top to bottom, colors are:
Red, Yellow, Green, Cyan, Blue, Magenta, Black
Estimated maximum without saturation is 60 kADU.
Fig 3. Photometric Profil around heavely saturated star with blooming
Centered on green line
From top to bottom, colors are:
Red, Yellow, Green, Cyan, Blue
Note the very different scale in X.
The large ring comes from reflects inside the optics.
It has a low spatial frequency (corresponding to 82 pixels).
By itself, it will probably have only a moderate incidence on the higher spatial frequency of the PSF, but it will contribute by the photon noise it adds to the image, reducing the S/N ratio for objects falling on the ring.
For any comment or question, mail to Jean-Claude PELLE
Updated 24 nov. 2001