An optical microscope can be converted by the user quickly with a few movements of the hand so that it can be used as an upright variant or as an inverted variant. The required optical elements are accommodated in components that can be mechanically separated from one another and variously combined. The optical system is calculated in such a way that an upright microscope with vertical illumination or transmitted illumination or an inverted microscope with vertical illumination or transmitted illumination results when the components are combined in the required manner by interfaces provided for this purpose.