A method and a device for the reduction of margins of the light image of a headline, and the headline incorporating the device, is provided, having a reflective diaphragm which is adapted to be shifted in a light axis direction within adjustment limits of a longitudinal position. The margins of the light image can be detected by an optical colour-sensitive photometric sensor, and colour characteristics of the light image margins can be evaluated by identifying a current position of the reflective diaphragm. The reflective diaphragm can then be fixed in the longitudinal position corresponding to selected colour characteristics of the light image margins. The reflective diaphragm can also be adapted to be shifted in a direction perpendicular to the light axis direction.