An endoscopic optical system including: a fiber image conductor arranged in an elongated shaft tube, the fiber image conductor having a proximal face； an objective arranged distally relative to the fiber image conductor； an observation device arranged proximally relative to the proximal face of the fiber image conductor； a mask； and a transparent cover pane arranged between the proximal face of the fiber image conductor and the observation device； wherein the transparent cover pane is configured as a moire filter.
