Adjustable pinhole, particularly for the illumination beam path and/or detection beam path of a laser scanning microscope, wherein the pinhole is defined by foil edges which are adjustable relative to one another, and at least two foils, each with at least one straight edge, are advantageously arranged relative to one another and/or connected to one another in such a way that their edges describe an L-shape and the L-shaped connection pieces are arranged on one another in such a way that they define a rhombic or square light passage and they are moved relative to one another for adjusting the pinhole.