Camera device with resistive target

Claim 1

A camera device with a resistive target comprising a camera tube having a target which in operation receives the energy emanating from the subject on one of its surfaces and which has the property of showing at each point between its two surfaces a dielectric polarisation governed by the energy absorbed by that point, means for generating inside said tube a beam of electrons issuing from a cathode and scanning point by point the other surface of said target so as to bring these points to the potential of said cathode and associated means for reading the signal current of flow of electrons deposited at each point of the target by said beam to obtain this potential, said tube comprising in its interior a first grid arranged in the vicinity of said cathode controlling the intensity of said beam, a heated ionisable gas reservoir made of a material of which the absorption capacity for said gas and hence the pressure of said gas in the tube is governed by its temperature, ions being generated in said tube by collision between the electrons of said beam and the molecules of said gas, and another grid arranged in the vicinity of said target and brought to a positive d.c. potential which is fixed in relation thereto, said camera device being characterised in that it comprises means for controlling the generation of said ions in the tube in dependence upon the average value of the target currents over a given period.