The photosensitive layers of photoelectric transducers all exhibit substantial spatial differences in sensitivity over the area of the layer. Sharply focused beams therefore cause undesired changes in the output signal given the slightest movements due to vibration, thermal expansion etc. Independently of the cross-section of the incident beam, instead of the focal point the condenser according to the invention images a closed trace on the layer, so that the sensitivity dispersion is averaged out. |