An optical system including: a sideways-viewing, distal optical assembly including an entry lens, a deflecting unit configured as a prism unit, and an exit lens on a common optical axis； a proximal optical assembly including left and right lens system channels, wherein the right and left lens system channels are identically configured and parallel to each other and each having an optical axis； and a prism unit between the distal optical assembly and the proximal optical assembly, the prism unit couples a left beam path exiting the exit lens into the left lens system channel and a right beam path exiting the exit lens into the right lens system channel； wherein a second distance between the left and right lens system channels is adjustable, the second distance being in a direction perpendicular to the first and second optical axes of the respective first and second lens system channels.
