Abstract: In an image tube, a photocathode is disposed to receive a photon image for emitting into the tube a corresponding electron image which is accelerated by an accelerating anode and focused upon an output device, such as a fluorescent screen or a microchannel electron multiplier. A gating electrode is interposed along the beam path between the anode and the output device. The potential difference between the photocathode and the gating electrode is periodically pulsed such that the gating electrode is sufficiently negative relative to the potential of the photocathode for reflecting the image electrons passing through the anode back to the anode for collection thereof and thus for gating off the electron image to the output device. This potential difference may be pulsed by pulsing the photocathode positive with respect to the gating electrode or by pulsing the gating electrode negative with respect to the photocathode.