ABSTRACT
Light from the lens could enter the enclosure through a window and land on the mosaic, releasing electrons which were attracted away towards the anode. Thus, a positive charge image built up on the surface of the mosaic. The charge was proportional to the intensity of light. The electron gun fired electrons in a raster scan at the mosaic. Any positive charge was cancelled by absorption of electrons from the beam. This absorption was detected by the conductive plate and output as a signal at the signal electrode. The rest of the electrons bounced off the mosaic to be picked up by the anode and were drawn away to the anode electrode. The Ionoscope used a high voltage between the electron
gun and the anode. This resulted in a high-velocity electron beam, which tended to ‘splash’ off the mosaic surface, causing what is termed secondary emission. This tended to reduce the tube’s ability to catch all the electrons released purely by photoemission. The Ionoscope’s geometry was not ideal. It was difficult to
focus the electron beam because it was striking the mosaic at an angle. The angled electron gun also made it difficult to produce an accurate raster scan. The Orthicon tube design helped eliminate these deficiencies.
3.3.1.3 The Orthicon tube
