Abstract: A counting device that detects intensity differences in reflections coming from stacked thin objects. The device comprises a radiation source generating a radiation beam and a photoelectric detector detecting the intensity differences in the radiation reflected by the objects, and is provided with an optical pathway placed between the objects and the photoelectric detector. The optical pathway comprises a diaphragm having a diaphragm opening which, in relation to the dimension of the beam of reflected radiation reaching the diaphragm, is smaller.