An apparatus and technique for measuring the electrical capacitance between a conducting tip of a scanning probe microscope and a sample surface is described. The housing has fluid ports, including a well formed over at least one port. A tubular rotor is disposed in the dispersion chamber and partitions the treatment gap into an outer gap portion and an inner gap portion. The novelty of the turning apparatus according to the invention is that the turning apparatus has selection means, which makes the turning process selective, and means ensuring that the process operates in parallel and synchronously with the object conveyor. Another of the probes operates as a receiver probe for sensing the electrical field and producing an output signal having an output property that is dependent at least in part on the source signal and the moisture content within the volume. It is thereby possible to achieve an image pickup apparatus capable of detecting and correcting at high accuracy those fault pixels occurring afterwards because of changes due to the passage of time or those fault pixels transiently occurring under certain modes.