Improved microphotometry by compensating for fluctuations in the illumination

Behind a beam-splitter in the illuminator, the irradiation of an area conjugated to the object plane is measured by a silicon photodiode and used as a reference signal. Analog division of the photomulitplier signal by this reference acts like stabilizing the light source by a factor greater than 25. A technical realization of the optical and electronical components as well as experimental results are described.