Abstract: A device for measuring the optical turbidity, i.e., the soot components in discharge gases of diesel engines, which is relatively simply constructed, operates safely and enables a simple handling even with differently structured measuring devices. This result is achieved in that a controller for controlling the light density of the measuring light beam is optically coupled with a light source. A sample and hold circuit is provided with the values of a measuring detector and the control detector fed to a sample and hold circuit in a time multiplex manner with the measuring values processed in a computer unit. Control values are fed to the light source by means of a control loop. In addition, the computer unit is capable of storing a plurality of measuring values or turbidity values and average value of the stored peak values, whereby the peak values are determined by a dynamic measuring of a defined number of measuring cycles.