Fig. 6.

Current measurement error is compared to measurement error if the system changed CCD gain settings to 1 or a Gaussian-weighted centroider. Measurement error is plotted as a function of total photons per sub-aperture, which varies across the aperture and between subjects. The red vertical dashed line indicates the average total photons per sub-aperture for subject 13, while the blue is for subject 17. Clearly one reason for poor performance of the AO system with some subjects is a decrease in total photons reflected from the eye resulting in increased measurement error.