  The performance metrics of different centroiding algorithms at low light
level conditions were optimized in the case of a Shack Hartmann Sensor (SHS)
for efficient performance of the adaptive optics system. For short exposures
and low photon flux, the Hartmann spot does not have a Gaussian shape due to
the photon noise which follows Poissonian statistics. The centroiding
estimation error was calculated at different photon levels in the case of
changing spot size and shift in the spot using Monte Carlo simulations. This
analysis also proves to be helpful in optimizing the SHS specifications at low
light levels.
