An imaging optical instrument with an optical system establishing an observation beam (18), and illuminating device generating a lighting beam (8), a slot-like observation diaphragm (13) moving in an intermediate image plane of the observation beam (18) and a slot-like lighting diaphragm (3) moving synchronously in an intermediate image plane of the lighting beam (8), in which the observation beam (18) and the lighting beam (8) meet obliquely on the object plane (10) and the slot images of the observation diaphragm (13) and the lighting diaphragm (3) substantially coincide in the object plane (10).
