Television Pick-up Tubes Research Articles

Television Pick-up Tube for both Light and X-Ray Pictures

INVESTIGATIONS carried out on television camera tubes using the photoconductive effect for converting a light image into an electrical signal have resulted in the development of an experimental tube sensitive to both visible light and to X-rays.

ビディコンの残像測定装置

ビディコンの残像測定装置

A small high-velocity scanning television pick-up tube

A small high-velocity scanning television pick-up tube

Photoconductivity in Vacuum Coated Selenium Films*

Photoconductive layers which have a dark resistivity higher than 1012 ohm×cm, are of particular interest for electrophotography and television pick-up tubes. Selenium coatings prepared by vacuum evaporation are suited for these purposes. At base plate temperatures lower than 50°C, vitreous selenium is deposited which shows photoconductivity for wavelengths shorter than 600 millimicrons. At higher coating temperatures, many small hexagonal selenium crystals embedded in the vitreous matrix are introduced. Both the nucleation and velocity of crystal growth are investigated. A small percentage of crystalline selenium produces an additional red sensitivity, while high dark insulation qualities are preserved. The incident light causes positive holes from the hexagonal crystals to be injected into the vitreous selenium. A small addition of tellurium induces at low coating temperatures a shift of the photosensitivity towards longer wavelengths. At higher temperatures coatings with fairly panchromatic response can be produced.

A small high-velocity scanning television pick-up tube

The results of an attempt to scale down a high-velocity scanning tube of the Super-Emitron type, without loss of sensitivity, is described. The pick-up tube so constructed has a performance superior to that of its predecessor and is about two or three times more sensitive. The superiority is due to increased mosaic storage, which reduces the shading signal but increases the picture lag. This is unnoticeable, except for very rapidly moving objects. The tonal gradation of the picture which the tube produces is satisfactory when viewed on modern cathode-ray tubes.

A review of some television pick-up tubes

A review of some television pick-up tubes

TV用撮像管に就て

TV用撮像管に就て

The authors' replies to the discussion on “A review of some television pick-up tubes” and “The design of a television camera channel for use with the C.P.S. Emitron”

The authors' replies to the discussion on “A review of some television pick-up tubes” and “The design of a television camera channel for use with the C.P.S. Emitron”

A review of some television pick-up tubes

The performance characteristics of some television pick-up tubes that have been used in practice in the past are reviewed critically. This review covers the Emitron, Super-emitron and orthicon. In the light of the experience gained in actual use of television cameras, an attempt is made to draw up a specification for an ideal pick-up tube.The C.P.S. Emitron (cathode-potential-stabilized Emitron) is then described. This description covers the general design of the tube, the technique of manufacture, the method of operation and the details of its performance characteristics. These are discussed with reference to the specification of the ideal tube and the performance of the actual tubes that have been described in this paper.

Discussion on “A review of some television pick-up tubes” and “The design of a television camera channel for use with the C.P.S. Emitron” before the Radio Section, 12th April, 1950

Discussion on “A review of some television pick-up tubes” and “The design of a television camera channel for use with the C.P.S. Emitron” before the Radio Section, 12th April, 1950

Distant Electric Vision

An outline of the history of television is followed by a detailed description of the design and development of some English television pickup tubes.

Limiting Resolution in an Image-Orthicon-Type Pickup Tube

An analysis is made of some of the factors which limit resolution in a television pickup tube of the image-orthicon type. Particular attention is given to effects of the glass-target characteristics and to departure from perfect focus in the image section, resulting from electron-emission velocities. It is shown that, as the width of lines in a resolution pattern is reduced, the signal generated tends to take the form of a small periodic modulation superimposed on a constant signal. This gives, in the reproduced image, a gradual reduction in contrast. A quantitative determination of limiting resolution, expressed as a number of lines, depends upon a physiological evaluation, not as yet available, of the minimum contrast in the reproduced image which will permit the pattern to be recognized as having a multiplicity of separate lines rather than a continuous blur. The general effects of target thickness and of color of incident light discussed herein have been confirmed experimentally.

New Television Field-Pickup Equipment Employing the Image Orthicon

A brief review of the characteristics of the more widely used types of electronic television pickup tubes traces the trend toward greater sensitivity, culminating in the image orthicon. This development results in the present-day ability to televise an unlimited variety of subject matter. Former restrictions imposed by requirements for large amounts of illumination have been almost entirely removed. An important by-product of higher sensitivity is the possible increase in depth of focus of the optical system. Field or portable equipment has been designed to take advantage of the improved characteristics of the image orthicon. It is a design which lends itself to a maximum of flexibility for various types of operation, including use in studios and in mobile units. Most of the units are shaped like a medium-sized suitcase. The camera includes a four-position lens turret and an electronic view finder. Camera cables may be as much as 1000 feet long. Electrical interconnections are simple and few in number. Each of the major units is described in some detail, along with its function in the system. Discussion of some of the unusual circuits is included in the Appendix.

The Motion of Electrons Subject to Forces Transverse to a Uniform Magnetic Field

The paths of electrons in a uniform magnetic field, under the influence of forces transverse to the magnetic field, are of interest in a variety of vacuum tubes. In general, the force experienced by the electron varies with time. The time variation may arise from motion of the electron through an electrostatic field, from motion of the electron along the lines of a curved magnetic field (inertial forces), or from the deliberate application of a time-varying electric field. A graphical method for obtaining the electron paths is described as follows; the given transverse-field versus time curve is approximated by tangent sections; the complete analytic solution is obtained for any tangent section; the analytic solution is interpreted graphically; and a method for joining graphical solutions of neighboring sections is developed. Emphasis is placed on the resultant velocity components and displacement after the field has ceased to act. The graphical method is used to analyze the motion of electrons in the orthicon and image orthicon, television pickup tubes in which the velocity components of the scanning beam critically affect performance. Problems considered are: magnetic and electrostatic deflection in a magnetic field, an electrostatic lens immersed in a magnetic field, the effect of "tapering" the applied forces, and the possibility of canceling unwanted velocity components introduced in one part of the tube by equal and opposite components introduced in another part.

The Image Orthicon-A Sensitive Television Pickup Tube

The image orthicon is a television pickup tube incorporating the principles of low-velocity-electron-beam scanning, electron image multiplication, and signal multiplication. It closely approaches the theoretical limit of pickup tube sensitivity and is actually 100 to 1000 times as sensitive as the iconoscope (1850) or orthicon (1840). It can transmit pictures with a limiting resolution of over 500 lines and, if properly processed, is relatively free from spurious signals. At low lights, the signal output increases linearly with light input; at high lights, the signal output is substantially independent of light input. The tube is completely stable at all light levels. The signal output is sufficiently high to make the operation of the tube insensitive to many of the preamplifier characteristics that are normally considered significant. The construction, operation, electron optics, and performance of the tube are discussed.

The Relative Sensitivities of Television Pickup Tubes, Photographic Film, and the Human Eye

The threshold scene brightness which a picture-reproducing device can record, a measure of its "operating sensitivity," depends not only upon the lens speed and the exposure time, but also upon the amount of detail in the recorded image. A general expression for the "operating sensitivity" of a picture-reproducing device is obtained which includes these factors together with the threshold number of quanta per picture element. This parameter characterizes the "true sensitivity" of the given device. The "true" and "operating" sensitivities of four types of television pickup tubes, photographic film, the human eye, and an ideal picture-reproducing device are obtained. Eye and film have of the order of one one-hundredth the "true sensitivity" of an ideal picture-reproducing device. Some recent television pickup tubes have of the order of one one-hundred-thousandth the "true sensitivity" of an ideal device. To compare "operating sensitivities," the same exposure time and equivalent lens systems are taken for the three devices. A television pickup tube which has a photoelectric response of 10 microamperes per lumen and makes full use of the storage principle can record scenes with no more illumination than that required by some of the "faster" photographic films. The relatively low "operating sensitivity" of film results from the large amount of intrinsic picture detail (a picture element is taken to be a single grain). The human eye has a range of "operating sensitivities" extending from that of film to a value several thousand times higher.

Television Pickup Tubes Using Low-Velocity Electron-Beam Scanning

Television pickup tubes which use a low-velocity electron beam for scanning a photosensitive target offer the possibility of avoiding some of the limitations of devices which use a high-velocity beam. Some of the advantages of the low-velocity beam are: (1) low level of spurious signals, (2) high maximum signal output, and (3) high efficiency of conversion of light into signal. The major problems encountered are: (1) ways to keep the beam in focus and (2) ways to obtain undistorted scanning of the photosensitive target. One solution to the difficulties of low-velocity-beam scanning involves the use of a uniform axial magnetic field to guide and focus the beam near the target. Because of this magneticfield, the usual type of deflection plates or deflection coils cannot be used to advantage. Two types of scanning which may be used are: (1) the release by a flying light spot of a beam of photoelectrons from successive points on a photocathode already immersed in the magnetic field and (2) the displacement of a beam from a thermionic cathode by a pair of defiection plates or coils operating in conjunction with the axial magnetic field and having an aperture at least as wide as the target to be scanned. Developmental television pickup tubes using each of these types of scanning with low-velocity electrons were tested and found to give the low spurious signal, high signal output, and high efficiency which had been expected.

A Television Pickup Tube

A television pickup tube is described which combines in one device the principles of signal storage, as in the Iconoscope, and of signal multiplication by secondary-electron emission. Calculations indicate that for a given video-frequency signal, this tube will generate a considerably greater electrical signal than any other present pickup device.

Television Pickup Tubes with Cathode-Ray Beam Scanning

Television pickup tubes which use cathode-ray beam scanning, although only one class of television pickup devices, may be made in a variety of ways, a number of which are described in this paper. In these tubes, the function of the electron beam is to release secondary electrons from the target, the number escaping being modulated by electrostatic fields, magnetic fields, orientation of electrodes or changes in the secondary emission ratio of the target. The Iconoscope is a well-known example of modulation by electrostatic fields produced by photoemission from the target. A conducting photocathode when used as a target, however, acted as if its secondary emission ratio were decreased by light. A copper plate oxidized and treated with caesium transmitted a picture with some time lag. Photoconductive materials exposed to light and scanned by an electron beam were made to develop potential variations over their surface and thereby transmit a television picture. Aluminum oxide and zirconium oxide, treated with caesium, were used in this manner. Selenium, used as a photoconductive material, also transmitted a picture. Germanium used as a target sensitive to heat radiation was able to transmit a picture, probably as a result of some thermoelectric effect. The most sensitive tubes tested were those in which an electron picture was focused upon a scanned, secondary electron emissive target. The scanning and picture projection operations may be separated by using a two-sided target. Coupling between the two sides was obtained by conducting plugs through the target.