Abstract: The power in the bucket (PIB) and b -parameter are chosen as criteria for characterizing the beam quality, the effect of the spherical aberration coefficient and obscure ratio of an annular lens on the super-Gaussian beam quality is analyzed. It is shown that there are different PIB curves at the geometrical and real focal planes, and by a suitable choice of the parameter of negative spherically aberrated annular lens the better power /energy focusability can be achieved as compared with the annular lens without spherical aberration.