On-axis wavefront error as a function of NGS magnitude in two different seeing conditions (median 1.1" and excellent 0.7"). The crossover point between NGS-AO and LGS-AO performance occurs at around V=11.5. Note that the LGS system can only track tip/tilt stars with V<17.5.
Ensquared energy in a 240 mas spaxial, as a function of NGS magnitude.