Disclosed is an illumination system for an ophthalmic surgical microscope (10), including a light source (32) for emitting light along an illumination beam path (50) directed toward an eye (12) of a patient, and a measuring device (54, 62) for measuring a parameter of the patients eye (12). The illumination system further includes an adjustable optical element (48) which allows the orientation of the illumination beam path (50) to be adjusted relative to an observation beam path (16L) of the surgical microscope (10) so as to obtain a red reflex, and a control device (60) which determines a red-reflex-optimized control parameter based on the measured parameter of the patients eye (12) and adjusts the optical element (48) according to the red-reflex-optimized control parameter.
