An electric field measuring equipment with a capacitive probe of 40 &mgr; resolution was constructed using only ordinary materials and techniques. The operation of this equipment was completely automatic and the electric field profiles were recorded continuously by anx‐yrecorder. The duration of one measurement, consisting typically of the recording of about 50 profiles and of the sample current vs time diagram, in 4 mm long samples, was [inverted lazy s] 50 min. The usefulness of this equipment has been proven through its use for the observation of a large number of new electric field domain formations in photoconducting CdS samples. The detailed description of these observations will be reported elsewhere.