An optical system of a microlithographic projection exposure apparatus designed for an operating wavelength of at least 150 nm. In one disclosed aspect, the optical system includes an element (11, 21) producing an angular distribution for light incident during the operation of the optical system and a fly's eye condenser (200, 400, 500) which includes two arrangements (210, 220, 410, 420, 510, 520) following one another in the light propagation direction and made of beam-deflecting optical elements (211-213, 221-223, 411-413, 421-423, 511-513, 521-523), which produce a multiplicity of optical channels. No optical element with refractive power is arranged in the beam path between the element (11, 21) producing an angular distribution and the fly's eye condenser (200, 400, 500).