Microscope with low distortion errors

Beam deflection units in light scanning microscopes are usually arranged in the objective pupil conjugate planes. The scanning optics which is required to generate the conjugate pupil planes is complex and not very light-efficient as it needs to compensate for different aberrations such as field curvature and lateral chromatic aberration. The invention is to offer a better image quality, simpler adjustment and a lower light loss. For this purpose, the optical system comprises a concave mirror (36) for imaging a respective point of the first and second beam deflecting unit (30A, 30B) to each other, wherein the concave mirror (36) and the first beam deflecting unit (30A) and the second beam deflecting unit (30B) are arranged so that the illumination beam path at the concave mirror (36) is accurately reflected once and a while by the concave mirror (36) caused first distortion and by the first and the second beam deflecting unit (30A, 30B) caused second distortion of the imaging each other at least partially compensate.