in a method and an apparatus for locating an examination size for diaphanoscopic examination of a living subject , a region of the living subject wherein the optimum examination location is suspected is sequentially transilluminated with radiation , preferably in a wavelength range of the optical tissue window , for registration of scattered light distributions in the form of location - related spread functions , particularly point spread functions , and at least one function - specific , location - related feature of each spread function is determined , based on which a position value defining the examination location is determined .