US3801849A

US3801849A - Variable magnification image tube

Info

Publication number: US3801849A
Application number: US00846107A
Authority: US
Inventors: J Edgecumbe
Original assignee: Varian Associates Inc
Current assignee: DKP A Corp OF; Intevac Inc; Varian Medical Systems Inc
Priority date: 1969-07-30
Filing date: 1969-07-30
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02

Abstract

A variable magnification image intensifier tube (zoom tube) is disclosed. The zoom tube includes a photocathode for converting a photon image into an electron image. An image converter screen is provided for converting the electron image into an intensified optical image for viewing or use. A focus electrode, a zoom electrode and an anode electrode, are positioned between the photocathode and the image converter screen for accelerating and focusing the electron image upon the image converter screen. An electron entrance opening in the zoom electrode is dimensioned so that the electron image pattern incident on the image converter screen is in focus at both the high and low ends of the magnification range for essentially the same magnitude of focus potential applied to the focus electrode, whereby the tube does not require refocusing upon shifting from one end of the magnification scale to the other.

Description

U nite States Patent Edgecumbe Apr. 2, 1974 VARHABLE'MAGNIFICATION IMAGE TUBE Primary Examiner-J-l'erman Karl Saalbach 7s lnventor: John Edgecumbe, Upland, Calif. Atwmey, A88, Cole;

Pressman; Robert K. Stoddard [73] Assignee: Varian Associates, Palo Alto, Calif. I22] Filed: July 30, 1969 [57] ABSTRACT [2]] Appl. No.2 846,107 A variable magnification image intensifier tube (zoom tube) is disclosed. The zoom tube includes a photocathode for converting a photon image into an elec- [52] US. Cl 313/102, 313/94, 313/65 R, tron image An image converter Screen is provided for 313/82 315/15 converting the electron image into an intensified opti- [51]" Int. Cl H103 29/46, H10 2 9/00 7 cal image for viewingflor useiA focus electrode. [58] Field of Search 313/102, 65 R, 94, 101 Zoom electrode and an anode electmde, are posi tioned between the photocathode and the image con- [56] References C'ted verter screen for accelerating and focusing the elec- UNITED STATES PATENT tron image upon the image converter screen. An elec- 2,946,895 7/1960 Stoudenheimer et al 313/101 x tron entrance opening in the zoom electrode is dimen- 3,082,342 3/1963 Pietri 313/94 X sioned so that the electron image pattern incident on 3,441,786 4/1969 y /65 R X the image converter screen is in focus at both the high NCIlSOII X and low ends of the magnification range for essentially gpg i i the same magnitude of focus potential applied to the c agen e a 3,474,275 10/1969 Stoudenheimer et al 313/65 ."l the tube does r r l re ocusmg upon sh1ft1ng from one end of the magnification scale to the other.

5 Claims, 6 Drawing Figures 0\/. Vi I 151w 0 12.5 KV.

I5 KV.

26 5 6 ANODE lMAGE IJECT RQQI E CONVERTER SC IROE EN PHOTO 25 CATlODE 19 PMENFEBAPR 2 I974 3.801., 8 19 H. a W.

F +5 TO-IOOV.

IMAGE CONVERTER SCREEN :0

CATHODE lg 24 6 2005 FIGZ VPN PRIOR ART m F 3 IOO- 500- O 3 z m 200- -m0- MAGNIFICATION 8 m ZOOM ELECTRODE .3 {of gF flgi g MAGNIFICATION .5 |.0 400 MAGNIFICATIONK 5 Z00- Q Z BE 5 MAGNIFICATIQLN .5 L0 [ld/ m, FOCUS ZOOM ELECTRODE ELECTRODE FE INVENTOR.

w i JOHN EDGECUMBE f; j BY WM fwm 7 ATTORNEY VARIABLE MAGNIFICATION IMAGE TUBE DESCRIPTION OF THE PRIOR ART Heretofore, variable magnification image intensifier tubes (zoom tubes) have been constructed with a focus electrode, a zoom electrode and an anode electrode, disposed intermediate the photocathode and the image converter screen. The magnification of the converted image in such zoom tubes has been variable from a low range to a high range by varying the potential applied to the zoom electrode. However, one of the problems with this prior art zoom tube has been that the focus voltage required to focus the electron image on the image converter screen was substantially different at the low end of the magnification range as opposed to that at the high end of the magnification range. Thus, when zooming the prior art zoom tube from one end of the magnification range to the other, the tube required refocusing by adjustment of the voltage applied to the focus electrode. It would be desirable to provide a zoom tube which may be zoomed from one end of the magnification range to the other without the requirement for refocusing.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of a variable magnification image intensifier tube having improved electron optics.

One feature of the present invention is the provision, in a variable magnification image intensifier tube having a focus electrode, a zoom electrode and an anode, of dimensioning the electron entrance opening in the zoom electrode so that the electron image pattern incident on the image converter screen is in focus at both the high and the low ends of the magnification range for essentially the same magnitude of focus potential applied to the focus electrode, whereby the tube does not require refocusing upon zooming from one end of the magnification range to the other.

Another feature of the present invention is the same as the preceding feature wherein the transverse dimensions of the electron entrance opening in the zoom electrode are smaller than those dimensions for such an opening which would yield a lower focus potential at the high end of the magnification range than at the low end of the magnification range.

Another feature of the present invention is the same as the first feature wherein transverse dimensions of the electron entrance opening in the zoom electrode are larger than those dimensions for such an opening which would yield a higher focus potential at the high end of the magnification range than at the low end of the magnification range.

Another feature of the present invention is the same as any one or more of the preceding features wherein the focus electrode is connected to the photocathode and operated at a constant potential, whereby the complexity of the zoom tube is substantially reduced.

Other features and advantages of the present invention become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal sectional view of a variable magnification image intensifier tube incorporating features of the present invention,

FIG. 2 is a plot of focus potential versus magnification depicting a typical focus voltage characteristic for a prior art image intensifier tube,

FIG. 3 is a plot similar to that of FIG. 2 depicting the focus voltage characteristic of an image intensifier tube incorporating the improved electron optics of the present invention,

FIG. 4 is a plot of focus potential versus magnification for a prior art variable magnification image intensifier tube having optics dimensioned such that the required focus potential increased from the low magnification end of the range to the high magnification end of the range,

FIG. 5 is a plot similar to that of FIG. 4 depicting the improved focus characteristics obtained by the electron optics of the present invention, and

FIG. 6 is an alternative embodiment of a portion of the image intensifier tube of FIG. 1 delineated by line 66 and incorporating features of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown a variable magnification image intensifier tube 1 incorporating features of the present invention. The tube 1 includes a vacuum envelope structure 2 having a faceplate structure 3 closing off one end and an image converter screen 4 closing off the other end of the vacuum envelope 2.

The faceplate 3 includes a circular disc member made of a material which is transparent to photons of energy emanating from, scattered from, or reflected from an object 5 to be observed. Faceplate 3 may comprise a solid disc of material or may comprise a bundle of light pipes, such as glass fibers, for observing objects out of a line-of-sight path between the face of the image intensifier tube and the object. As used herein, photons are defined to include not only those photons within the visible spectrum but those within the invisible, such as in the infrared range and within the higher energy range such as x-rays, gamma rays, etc. The inside surface of the faceplate 3 is provided with a concave surface over which is deposited a transparent conductive film onto which is deposited a photocathode layer 6 which is responsive to the wavelength of the photon energy emanating from the object 5. One suitable photo cathode material includes a multi alkaline photocathode material, such as a composition of sodium, potassium, cesium and antimony. The faceplate disc 3, as of glass, is sealed to a metallic frame 7 as of Kovar which in turn is sealed to a sealing ring 8, as of Kovar, disposed at one end of the envelope 2.

The image converter screen 4 includes an optically transparent disc 9, as of glass or a bundle of glass fibers, having a conventional fluorescent phosphor material 10 which fluoresces upon being impacted by electrons deposited on an inside concave surface thereof and over which is deposited a thin conductive layer, as of aluminum. A typical phosphor would comprise, for example P-20 phosphor of zinc and cadmium sulfide particles. The transparent disc 9 is sealed to a metallic frame member 11, as of Kovar, which in turn is sealed, as by welding, to a Kovar frame member 12 provided at the end of the vacuum envelope structure 2.

A composite electrode structure is provided within the tube intermediate the photocathode 6 and the image converter screen 10 for focusing and accelerating the electron image emitted from the photocathode 6 onto the image converter screen 10 to produce an intensified optical image at the converter screen 10. The electrode structure includes an annular focus and gate electrode 13, followed by an annular zoom electrode 14, which in turn is followed by an annular anode electrode 15 conductively connected to frame member 12 for operation at the same potential as the image converter screen 10.

The focus and gate electrode 13, as of stainless steel, includes an electron entrance opening 16, at the end thereof facing the photocathode 6, and a constricted electron exit opening 17. The focus and gate electrode 13 is supported from the envelope 2 via the intermediary of an annular metallic frame member 18, as of Kovar, which forms a portion of the envelope 2 and a terminal for application of a focus potential, as of +300 to l volts relative to the photocathode 6, thereto. Frame 18 is insulated from the photocathode 6 via the intermediary of a cylindrical insulator section 19 of the envelope 2, as of glass.

The zoom electrode 14, as of stainless steel, has a constricted electron entrance opening 21 of a diameter d and which is disposed substantially in the plane of the constricted electron exit opening 17 in the focus and gate electrode 13. The downstream end of the zoom electrode 14 includes an electron exit opening 22 which is of constricted diameter compared to the mid portion of the zoom electrode. The zoom electrode 14 is carried from the vacuum envelope via an annular metallic frame 23, as of Kovar. The frame 23 is sealed into the vacuum envelope 2 via

annular glass insulators

24 and 25, respectively, to permit an independent potential as of +1.5 KV to +12.5 KV to be applied to the zoom electrode 14 relative to the photocathode 6.

The anode electrode 15, as of stainless steel, includes an electron entrance opening 26 of constricted inside diameter compared to the diameter of the remaining portion of anode 15. The electron entrance opening 26 of the anode 15 is positioned within the electron exit opening 22 of the zoom electrode 14.

In operation, electron images emitted from the photocathode 6 are focused by the focus electrode 13 through the entrance opening 21 in the zoom electrode 14 and thence focused through the electron entrance opening 26 of the anode onto the image converter screen 10. Such electron images are accelerated from zero potential to approximately 15 KV and strike the image converter screen with a relatively high energy to produce a substantial intensification of the converted optical image produced at the image converter screen 10 compared to the brightness of the image received by the photocathode 6.

The tube 1 is operable over a certain magnification range, as of from 0.3 to 1.0, in variable accordance with the potential applied to the zoom electrode 14 relative to the potential applied to the photocathode 6. More particularly, with a relatively low potential applied to the zoom electrode 14, as of +1.5 KV, the entire electron image obtained from the photocahtode 6 is focused over the entire surface of the image converter screen 10, whereas when a relatively high potential, approaching the anode potential, as of +12.5 KV, is applied to the zoom electrode 14, only approximately a central one-third of the electron image produced by the photocathode 6 fills the image converter screen 10.

It has been discovered that there is an optimum diameter d for the electron entrance opening 21 in the zoom electrode 14 which will permit varying or zooming the magnification from the low end of the magnification range, as of from 0.3, to the high end of the magnification range, as of 1.0, while allowing the same focus potential V, to be applied to the focus electrode 13 at both ends of the range. More particularly, in the prior art, the diameter d of the electron entrance opening 21 in the zoom electrode 14 was other than an optimum diameter such that the focus potential had to be changed for each different setting of the magnification and was different at both ends of the range. For example, when the diameter d of the electron entrance opening 21 was larger than the optimum diameter, the focus potential characteristic was as shown in FIG. 2, whereas when the diameter of the electron entrance opening 21 was smaller than the optimum diameter the focus potential characteristic was as shown in FIG. 4.

This prior art focus potential versus magnification characteristic was troublesome since when zooming the tube from one end of the range to the other the focus potential had to be changed to obtain a focus of the image. However, when the diameter d of the electron entrance opening 21 in the zoom electrode 14 is selected, during fabrication of the tube, to have the optimum diameter, the focus potential is the same at the low end of the magnification range as it is at the high end of the magnification range, as shown in FIGS. 3 and 5. For the focus characteristic as shown in FIG. 2, the optimum diameter for the electron entrance opening 21 in the zoom electrode 14 is decreased to obtain the characteristic for the optimum diameter, as shown in FIG. 3. When the focus potential characteristic is as shown in FIG. 4 the diameter 3 for the electron entrance opening 21 in the zoom electrode 14 is increased to obtain the characteristic as shown in FIG. 5. In a typical example, wherein the photocathode 6 had a diameter of 6 inches, the prior art electron entrance opening 21 of the zoom electrode 14 had a diameter of 1.65 inches. This resulted in a focus potential characteristic as shown in FIG. 2. By decreasing the diameter d of the electron entrance opening 21 of the zoom electrode from 1.65 to 1.00 inch the-focus characteristic was changed to that as shown in FIG. 3 such that the focus potential was the same at the low and high ends of the magnification range, thereby avoiding the necessity of refocusing tube on zooming from the low to the high end of the magnification range.

In the tube of FIG. 1 the structure is essentially a tetrode in that four independent potentials are applied to the electrode structures. The focus electrode 13 is also employed as a gate for gating on and off the electron image to the image converter screen 10 for controlling the gain of the image intensifier tube. The discovery of an optimum diameter for the electron entrance opening 21 in the zoom electrode 14 permits construction of a triode image intensifier tube, provided that gain control is not desirable. Such a triode construction is depicted in FIG. 6.

Referring now to FIG. 6, there is shown an alternative triode embodiment of the present invention wherein the structure is essentially the same as that of FIG. 1 except that the focus electrode 13 is conductively connected to the photocathode 6 and operated at photocathode potential. The focus electrode 13 is dimensioned relative to the dimensions of the zoom electrode 14 and to the dimensions of the photocathode 6 such that at one end of the magnification range, the focus potential is volts. The diameter d of the electron entrance opening 21 of the zoom electrode 14 is then dimensioned for the optimum diameter such that the 0 volt focus potential is the same at the high and low ends of the magnification range. In this manner a separate focus potential is not required and the construction of the tube is substantially simplified, In this embodiment, the annular frame member 8 is extended to the frame member 18 which in turn holds the focus electrode 13.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a variable magnification image intensifier tube, means forming a photocathode for converting a photon input image incident upon said photocathode into an electron image pattern emitted from said photocathode, an image converter screen for converting the electron image pattern into an intensified output optical image, means forming an electrode structure disposed intermediate said photocathode and said image converter screen for accelerating and focusing the emitted electron image pattern onto said image converter screen, said electrode structure including an anode electrode means, a zoom electrode means, and a focus electrode means, said zoom electrode means being disposed between said photocathode and said anode electrode for varying the magnification of the electron image incident on said image converter screen over a certain range of magnification having a high end and a low end in variable accordance with a potential applied to said zoom electrode means, said zoom electrode having an electron entrance opening and an electron exit opening through which electron images pass to said converter screen, said focus electrode means being disposed imtermediate said zoom electrode and said photocathode for focusing the electron image upon said image converter screen,

the improvement WHEREIN, the size of said electron entrance opening is dimensioned such that the electron image pattern incident on said image converter screen is in focus at both the high and low ends of said magnification range for substantially the same magnitude of focus potential applied to said focus electrode means.

2. The apparatus of claim 1 wherein said photocathode is concave having a concave surface facing said zoom electrode means, said focus electrode is annular having an electron entrance opening and an electron exit opening of smaller dimensions than said electron entrance opening in said focus electrode means, and wherein said electron entrance opening in said zoom electrode is positioned substantially at said electron exit opening of said focus electrode means and is of constricted transverse dimensions compared to the transverse dimensions of the midportion of the electron passageway through said zoom electrode means.

3. The apparatus of claim 2 wherein said anode electrode means is annular having an electron entrance opening and an electron exit opening, said electron entrance opening in said anode e lec t ro debeing of smaller trah sfiafse (ii r;e ions than said electronTit opening of said anode electrode, and said electron entrance opening of said anode electrode being disposed within the electron passageway of said zoom electrode means.

4. The apparatus of claim 1 wherein said transverse dimensions of said electron entrance opening in said zoom electrode are smaller than those dimensions for such an opening which would yield a lower focus potential at the high end of the magnification range than at the low end of the magnification range.

5. The apparatus of claim 1 wherein said transverse dimensions of said electron entrance opening in said zoom electrode are larger than those dimensions for such an opening which would yield a higher focus po' tential at the high end of the magnification range than at the low end of the magnification range.

Claims

1. In a variable magnification image intensifier tube, means forming a photocathode for converting a photon input image incident upon said photocathode into an electron image pattern emitted from said photocathode, an image converter screen for converting the electron image pattern into an intensified output optical image, means forming an electrode structure disposed intermediate said photocathode and said image converter screen for accelerating and focusing the emitted electron image pattern onto said image converter screen, said electrode structure including an anode electrode means, a zoom electrode means, and a focus electrode means, said zoom electrode means being disposed between said photocathode and said anode electrode for varying the magnification of the electron image incident on said image converter screen over a certain range of magnification having a high end and a low end in variable accordance with a potential applied to said zoom electrode means, said zoom electrode having an electron entrance opening and an electron exit opening through which electron images pass to said converter screen, said focus electrode means being disposed imtermediate said zoom electrode and said photocathode for focusing the electron image upon said image converter screen, the improvement WHEREIN, the size of said electron entrance opening is dimensioned such that the electron image pattern incident on said image converter screen is in focus at both the high and low ends of said magnification range for substantially the same magnitude of focus potential applied to said focus electrode means.

3. The apparatus of claim 2 wherein said anode electrode means is annular having an electron entrance opening and an electron exit opening, said electron entrance opening in said anode electrode being of samller transverse dimensions than said electron exit opening of said anode electrode, and said electron entrance opening of said anode electrode being disposed within the electron passageway of said zoom electrode means.

5. The apparatus of claim 1 wherein said transverse dimensions of said electron entrance opening in said zoom electrode are larger than those dimensions for such an opening which would yield a higher focus potential at the high end of the magnification range than at the low end of the magnification range.