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The effects of hard apertures on the energy distribution, the far-field beam quality, the mode volume, and the discrimination against high-order modes in Cassegrain resonators with Gaussian reflectivity mirrors have been investigated both theoretically and experimentally. It has been shown that, in the far field, the fraction of energy in the secondary lobes remains small as long as the ratio of the design beam waist to the radius of the gain medium is <0.40. For , deterioration of the beam quality and diffraction losses counterbalanced a more efficient filling of the gain medium to limit the resonator efficiency. At low magnifications, resonators with Gaussian mirrors out perform resonators with Standard mirrors.