GB2132009A

GB2132009A - Apparatus for providing light bias for a camera tube

Info

Publication number: GB2132009A
Application number: GB08234968A
Authority: GB
Inventors: David George Holland; Robert Douglas Barr
Original assignee: English Electric Valve Co Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1982-12-08
Filing date: 1982-12-08
Publication date: 1984-06-27
Also published as: GB2132009B

Abstract

Light bias is provided for a camera tube 15 by fixing an annular disc 1, having an LED 9 attached, to pins 18 and 19 of the tube 15, the pumping stem 17 of the envelope 16 of the tube 15 extending through the centre of the disc 1. A light guide 21 provides a path for the light from the LED 9 to the region in the tube 15 where it is required. A resistor 14, also attached to the disc 1, has a predetermined value to give the required level of illumination. <IMAGE>

Description

SPECIFICATION Apparatus for providing light bias for a camera tube This invention relates to apparatus to provide light bias for a camera tube.

It is well known to provide light biassing for a camera tube, especially for one of the type having a target of lead monoxide. The light bias results in a low level ambient light condition, improving operating characteristics of the tube. Some examples of light biassed camera tube arrangements are described, for example, in the specification of our U.K.

patent number 1 573 558.

A difficulty which is experienced with prior arrangements is that associated with providing a convenient and satisfactory location for the required light source particularly since it is generally desirable to locate the light source within the overall outline of the camera tube.

This invention seeks to provide improved apparatus for providing light bias for a camera tube in which the above difficulty is mitigated.

According to this invention an apparatus for providing light bias for a camera tube comprises a disc having a light source attached to its surface, there being apertures in the disc corresponding to respective pins which extend from the base of the camera tube, such that when the apertures are located at the respective pins the light source is so positioned as to provide light bias.

Normally said light source will be positioned on said disc so as to be offset from the axis of said tube when said disc is positioned.

When the light source offset as described this will fit into existing space around the normally provided pumping stem of the camera tube. This is particularly advantageous where the camera tube is small, for example one which is included in portable equipment. The space required by the dics and its associated circuitry is available without alteration to the basic outline of the tube or its housing, enabling the tube, with light bias, to be used directly in existing cameras.

Normally the disc is annular, the stem of the tube passing through the central aperture therein.

It is preferred that the light source is a light emitting diode or LED. An LED requires appreciabiy less power to drive it than does a filament lamp. This is particularly advantageous where the camera is battery powered. It is also more compact than a filament lamp and does not require an additional socket in which to mount it.

Also it is preferred that a diode is included, electrically connected in series with the light source whereby by changing the direction of current flow in a circuit including the light source, said source may be switched on or off. This tends to be true in any case for an LED without a diode because of its directional properties but inclusion of the diode will give an additional safeguard.

According to a feature of the invention a camera tube arrangement comprises a camera tube and apparatus as described above. The disc may be arranged to be readily removable in service which facilitates the replacement of faulty components on the disc. This may be done by providing spring connections of some sort. Also if light biassing is not required for a certain usage the disc may simply be removed.

If the disc is to be incorporated in the arrangement permanently it may be soldered to the pins of the tube.

Preferably a light guide is included in the arrangement to provide part of a light path from the light source to that part of the camera tube that it is desired to illuminate. An optical cement or filler may be used between the light source and the base of the tube. A light guide may also be provided within the envelope of the tube itself. Where the light source is offset from the centre of the disc the light guide does not need to enter the restricted space of the pumping stem of the camera tube, but may be located in relatively free space at the side of the tube. The light source may be easily arranged close to one end of the light guide, giving good optical efficiency.

Preferably the light source is connected in parallel with a cathode heater of the camera tube when the apertures are located at the respective pins. Thus it may use the same supply as the heater and, if a diode is included or an LED is used, by changing the polarity of the heater supply the light source may be switched on or off.

The invention will now be further described by way of example with reference to the accompanying drawing in which: Figure 1 shows schematically a disc in accordance with the invention, and Figure2 illustrates a camera tube arrangement, with like references being used for like parts.

With reference to Figure 1, a thin annular planar disc 1 is of an opaque electrically insulating material and has seven apertures, 2, 3, 4, 5, 6,7 and 8. One surface of the disc bears an LED 9 and a diode 10. A first conductive track 11 laid down on the disc 1 connects the LED 9 with an aperture 3. A second conductive track 12 connects the diode 10 with another aperture 4. The first conductive track 11 is connected, at the end other than that at which it is connected to the aperture 3, to a third conductive track 13. The third conductive track 13 is laid down on the other surface of the disc 1 and is also connected to the second conductive track 12. Included in the third conductive track 13 is a thick film trimmable resistor 14.Those parts of circuitry on the other surface of the disc 1 than that to which the LED 9 is attached are illustrated in a broken line.

Referring to Figure 2 a photoconductive camera tube 15 has an overall generally cylindrical envelope 16, with a diameter of about 1.5 cm., which is evacuated and which has a pumping stem 17. The tube 15 has seven pins, extending from its base 20, of which only two 18 and 19 are shown. These two pins 18 and 19 are connected to a cathode heated located within the envelope 16. The seven apertures 2,3,4,5,6,7 and 8 of the disc 1 correspond to the seven pins of the tube 15 so that the disc 1 can be fitted over them, as shown in Figure 2. The disc 1 can in addition be fitted close to the base 20 of the tube 15 because its annular configuration permits the pumping stem 17 to extend through it.

The disc 1 is fitted on the pins so that the surface bearing the LED 9 faces towards the transparent base 20 of the tube 15. A light guide 21 is located within the envelope 16 near one of its walls, one end of the light guide 21 being arranged at that part of the base 20 at which the LED 9 is located. The other end of the light guide 21 is at that region of the tube 15 where the target 22 of the camera tube 15 is located and is arranged so that light passing through the light guide 21 is directed onto an etched surface 23 to give a diffuse ambient light within the tube 15.

The LED 9 is caused to switch on or off as required by reversing the polarity of the supply to the heater.

The desired level of illumination from the LED may be obtained by adjusting the value for the trimmable resistor 14, although it may be possible to vary the level in some other way, for example by altering the heater supply.

Although only one LED is employed in this apparatus it is possible to use more than one, having them spaced around the disc.

If the disc employed is transparent, or has further apertures, all the components may be attached to the surface of the disc arranged furthest from the base of the tube in operation.

Claims

1. Apparatus for providing light bias for a camera tube, comprising a disc having a light source attached to its surface there being apertures in the disc corresponding to respective pins which extend from the base of the camera tube, such that when the apertures are located at the respective pins the light source is so positioned as to provide light bias.

2. Apparatus as claimed in claim 1 and wherein the light source is a light emitting diode.

3. Apparatus as claimed in claim 1 or 2 and including a diode electrically connected in series with the light source whereby by changing the direction of current flow in a circuit including the light source, said source may be switched on or off.

4. A camera tube arrangement comprising a camera tube and apparatus as claimed in any preceding claim.

5. An arrangement as claimed in claim 5 and including a light guide to provide a part of a light path from the light source to that part of the camera tube that it is desired to illuminate.

6. An arrangement as claimed in claim 4 or 5 and wherein the light source is connected in parallel with a cathode heater of the camera tube when the apertures are located at the respective pins.

7. Apparatus substantially as illustrated in and described with reference to the accompanying drawing.

8. An arrangement substantially as illustrated in and described with reference to Figure 2 of the accompanying drawings.