An optoelectronic sensor for detecting an object in a monitored zone is provided that comprises a light transmitter for transmitting transmitted light, a light receiver having a plurality of light reception elements operable in Geiger mode for receiving transmitted light remitted in the monitored zone, a reception optics arranged upstream of the light receiver and having a diaphragm, and a control and evaluation unit that is configured to determine a distance from the object with reference to a received signal of the light receiver from a time of flight between the transmission of the transmitted light and the reception of the remitted received light, wherein the diaphragm comprises a diaphragm substrate having at least one metallic layer and one diaphragm aperture. In this respect, a contact region of the metallic layer for potential equalization is electrically conductively connected to another component of the sensor.