The apparatus (40) has a light-insulated housing (41) with a hollow space (42) and an aperture (43) for inserting a distal end (12) of an imaging device i.e. endoscope (10), into the hollow space. A reference surface (72) with predetermined optical properties is formed in the hollow space for remission of illuminating light directed onto the reference surface or for emission of fluorescent light. A positioning device (50) holds the imaging device at a predetermined position of the distal end of the imaging device in relation to the reference surface. An independent claim is also included for a method for testing an optical investigation system.
