Analysis of 20140320 data
Looking at Flux pattern of a single exposure on sky we notice a center-symmetric illumination (4000 in the center to 2000 at the edge).
Evaluating FWHM the map the values we get between 3.6 and 2.4asec on bottom right.
Controlled the same pattern in high flux (20000 counts) with the internal source, the illumination pattern changes (40000 on top right and 20000 on bottom left).
The FWHM map is very uniform varying between 0.68 to 0.75asec (lower left vs upper right edges).
Measurements in closed loop (jitter and pupil).
Light is hitting an edge of the field stop. The spots have a more uniform pattern. The light is brighter in the upper right edge.