Figure 10: (a) Sequence of artificial images of an = 8 star on the fiber viewing Unibrain 520b camera on Stella-II, exposure time set to 1 second. Pixel scale is 0.13 arcsec/pixel the diameter of the pinhole is 2.8 arc seconds. The seeing was set to 1 arcsec. (b) Recovering of the shift of the center of the star relative to the center of the pinhole, for the image sequence to the left. Center of gravity uses first image moments the quadrant method compares the ADU sum in the left-to-right and up-to-down image segments. These two methods do not deliver a true shift, but only a shift direction. For clarity, the direction has been scaled to match the true offset. Direct modeling of the star plus pinhole recovers the true shift and allows to estimate the light loss and seeing, but requires relatively high levels.