in a photoplotting apparatus and method using a flash lamp to expose a line on a photosensitive surface , and wherein the photohead has a number of apertures of different size to vary the width of the generated line , the quality of line drawn with each aperture is controlled by controlling or setting for each aperture the factor by which the flash rate of the lamp is related to the speed of the photohead . a signal representing the speed of the photohead over the photosensitive surface is divided by a division factor uniquely associated with the selected aperture to produce a flash rate command signal controlling the flash rate of the flash lamp . taking into account the dividing factor associated with each aperture , the speed of the photohead is limited to one at which the flash lamp flashes at or slightly below its maximum flash rate , thereby producing maximum throughput for the apparatus .