WO1995005716A1 - Surveillance system with image intensifier tube - Google Patents

Surveillance system with image intensifier tube Download PDF

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Publication number
WO1995005716A1
WO1995005716A1 PCT/US1994/009191 US9409191W WO9505716A1 WO 1995005716 A1 WO1995005716 A1 WO 1995005716A1 US 9409191 W US9409191 W US 9409191W WO 9505716 A1 WO9505716 A1 WO 9505716A1
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WO
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Patent type
Prior art keywords
image
image sensor
daytime
assembly
nighttime
Prior art date
Application number
PCT/US1994/009191
Other languages
French (fr)
Inventor
David B. Johnson
Allan W. Scott
Thomas M. Daley
Original Assignee
Intevac, Inc.
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00Details of television systems
    • H04N5/222Studio circuitry; Studio devices; Studio equipment ; Cameras comprising an electronic image sensor, e.g. digital cameras, video cameras, TV cameras, video cameras, camcorders, webcams, camera modules for embedding in other devices, e.g. mobile phones, computers or vehicles
    • H04N5/225Television cameras ; Cameras comprising an electronic image sensor, e.g. digital cameras, video cameras, camcorders, webcams, camera modules specially adapted for being embedded in other devices, e.g. mobile phones, computers or vehicles
    • H04N5/2251Constructional details
    • H04N5/2254Mounting of optical parts, e.g. lenses, shutters, filters or optical parts peculiar to the presence or use of an electronic image sensor

Abstract

A camera attachment converts a standard daylight video camera into a day/night-vision video camera. The attachment device, in one embodiment, contains an image intensifier tube (61) and a fiber optic image conduit (67), either of which may be switched into the optical path to receive and either amplify or simply conduct the light image to a relay lens (63). The relay lens (63) focuses the output image from either the image tube (61) or the fiber optic image conduit (67) onto the optical input of the video camera (64). The switching of the image intensifier tube (61) or the fiber optic image conduit (67) is dependent upon the ambient light conditions. In another embodiment, an image intensifier assembly (312) is rotated into the optical path between an input lens (310) and a CCTV camera (300) in the nighttime mode. The camera has a separate image sensor assembly (302) which is moved along the optical path to a position directly behind the input lens (310) in the daytime mode.

Description

SURVEILLANCE SYSTEM WITH IMAGE INTENSIFIER TUBE

Field of the Invention

The present invention relates generally to surveillance systems, such as closed-circuit security or industrial inspection television systems, and more particularly to a novel system capable of permitting either daylight or enhanced night "vision" which operates with natural light without added illumination.

Background of the Invention

Image intensified television cameras suitable for use in closed circuit television (CCTV) systems are of two basic types. One involves the use of image orthicon television cameras utilizing lenses to focus the image onto the camera. To achieve better low-light sensitivity, such cameras are often supplemented by infrared illuminators. The second type consists of a lens to focus light onto the photocathode of a night-vision image intensifier tube, the image intensifier tube, and a direct coupled CCD device (charge coupled device) television camera or a transfer lens to focus the output of the intensified image onto the CCD input of the video camera. At the heart of such a CCTV system is the light amplifier image intensifier tube (usually referred to as a generation or Gen I, II or III type device).

Image intensifier tubes (also called image enhancement tubes or simply image tubes) were first developed in the mid to late 1930's for military night vision applications. The early electro-optical low-light amplifiers were image converter infrared tubes, also known as Gen 0 and Gen I night amplifier tubes. These were used successfully for many years. A successor to these tubes was the microchannel intensifier. It was a great improvement in size, cost and performance. A microchannel intensifier tube basically consists of a photo-sensitive cathode, a microchannel plate (MCP), a phosphor output screen and means to create appropriate fields within the tube. The photocathode converts incoming photons representing an image to a corresponding spatially positioned stream of electrons. The electrons are accelerated to an MCP which intensifies the flow of electrons. At the output of the MCP, the intensified electrons are accelerated again by another strong electric field to strike the luminescent phosphor screen on which an enhanced visible image is created. The MCP consists of a two-dimensional array of miniature microchannel multipliers. A description of microchannel image intensifiers and the fabrication of microchannel plates can be found in "The Microchannel Image Intensifier," The Scientific American. Vol. 245 (November 1981 ) pp. 46-55 by Michael Lampton.

Microchannel image intensifiers are frequently employed today in applications requiring high amplification of extremely low light levels. One obvious advantage of the current generation of microchannel image intensifiers is their light sensitivity which obviates the need for auxiliary irradiation either in the visible or near-infrared spectrum. They are particularly suited to nighttime surveillance in military or police applications, since they have high luminous gain, high image resolution and excellent light sensitivity. In addition, Gen III tubes are particularly sensitive in the near-infrared (NIR) spectrum, which makes them particularly useful in nighttime surveillance since night sky radiation is particularly high in the non-visible NIR region.

Image intensifier tubes and cameras have improved over the years, and today there are probably 50 different low light level camera systems made by a dozen or more manufacturers. Notwithstanding this, there are drawbacks that limit use of modern image intensifier tubes, even in the case of the latest generation units. Although relatively inexpensive when compared to earlier systems, there are many surveillance and security applications where the marketplace cannot accept the $9,000 to $20,000 price of the individual image intensifier TV cameras. In addition to the initial acquisition cost, the annualized replacement costs of image intensifier tubes or SIT camera tubes (silicon intensifier target) are inordinately high due to their restricted shelf life and even shorter operating lifetime. The operating lifetime of these tubes is dramatically reduced by exposure to high light levels. Also applications requiring continuous (24 hours/day) operation can shorten useful lifetime considerably. Gating of the high-voltage power supply has been used to limit the on time of the tube in certain applications, but there are other tradeoffs with such modifications. Compounding the replacement cost is the difficulty of replacing an image tube. It is often mechanically bonded to the optics assembly and TV camera, requiring replacement of the entire system, or at the very least an involved and costly repair process. Summary of the Invention In accordance with one aspect of the present invention, a camera system for operation in daytime and nighttime lighting conditions without additional illumination is provided. The camera system comprises a video camera having an image sensor, an image intensifier assembly including an image intensifier tube, an input lens for receiving input light representative of an image, and a controller for switching between a nighttime operating mode and a daytime operating mode. In the nighttime mode, the image intensifier assembly is positioned on an optical axis between the input lens and the image sensor, and the image sensor is positioned to receive an image from the image intensifier assembly. In the daytime mode, the image intensifier assembly is removed from the optical axis and the image sensor is positioned along the optical axis to receive an image directly from the input lens.

Preferably, the controller comprises first means for moving the image intensifier assembly between a nighttime position on the optical axis and a daytime position removed from the optical axis, and second means for moving the image sensor forward and backward along the optical axis between a nighttime position for receiving an image from the image intensifier assembly and a daytime position for receiving an image directly from the input lens. In a preferred embodiment, the image intensifier assembly is mounted on a disk, and the disk is rotated such that the image intensifier assembly is moved into the optical axis in the nighttime mode. The image sensor of the video camera is preferably mounted in an image sensor assembly separate from an electronics assembly of the video camera. The image sensor assembly is moved forward and backward along the optical axis between the daytime and nighttime positions. In the daytime position, the image sensor assembly is located directly behind the input lens. In the nighttime position, the image sensor assembly is located directly behind the image intensifier assembly.

The image intensifier assembly typically inverts the image received from the input lens. The image sensor is preferably rotated by 180 ° between the daytime and nighttime positions to compensate for the image inversion by the image intensifier assembly. In addition to the image intensifier tube, the image intensifier assembly preferably includes a relay lens for transferring the image from the image intensifier tube to the image sensor in the nighttime operating mode. The image intensifier assembly may further include an expander lens for expanding the image formed by the input lens to match the image format of the image intensifier tube. The camera system may further include means for sensing an ambient light level. The controller may include means responsive to the sensed ambient light level for automatically switching to and between the nighttime mode and the daytime mode. According to another aspect of the invention, a method for performing surveillance in daytime and nighttime lighting conditions without additional illumination is provided. The method comprises the steps of providing a video camera including an image sensor, an image intensifier assembly and an input lens for receiving incoming light representative of an image, and switching between a nighttime operating mode and a daytime operating mode. In the nighttime mode, the image intensifier assembly is positioned on an optical axis between the input lens and the image sensor, and the image sensor is positioned to receive an image from the image intensifier assembly. In the daytime mode, the image intensifier assembly is removed from the optical axis, and the image sensor is positioned along the optical axis to receive an image directly from the input lens.

According to a further aspect of the invention, a camera system for operation in daytime and nighttime lighting conditions comprises an input lens for receiving incoming light representative of an image, a first video camera having a first image sensor, an image intensified camera assembly including an image intensifier tube and a second video camera having a second image sensor, and a controller for switching between a nighttime mode and a daytime mode. The second image sensor is positioned to receive an intensified image from the image intensifier tube. In the nighttime mode, the image intensifier tube and the second image sensor are positioned on the optical axis of the input lens. In the daytime mode, the first image sensor of the first video camera is positioned on the optical axis of the input lens. Preferably, the first video camera comprises a color CCTV camera, and the second video camera comprises a black and white CCTV camera.

The controller preferably comprises a disk for mounting the first image sensor and for mounting the image intensifier tube and the second image sensor, and means for rotating the disk between daytime and nighttime positions. The output of the first video camera is switched to a monitor during the daytime mode, and the output of the second video camera is switched to the monitor during the nighttime mode.

According to yet another aspect of the invention, a camera system for operation in daytime and nighttime lighting conditions without additional illumination comprises an input lens for receiving incoming light representative of an image, a first image sensor, an image intensifier assembly including an image intensifier tube and a second image sensor, a camera electronics assembly and a controller for switching between a nighttime mode and a daytime mode. The second image sensor is positioned to receive an intensified image from the image intensifier tube. In the nighttime mode, the image intensifier assembly is positioned on the optical axis of the input lens, and the second image sensor is coupled to the camera electronics assembly. In the daytime mode, the first image sensor is positioned on the optical axis of the input lens and is coupled to the camera electronics assembly. Brief Description of the Drawings

For a better understanding of the present invention, reference is made to the accompanying drawings, which are incorporated herein by reference and in which:

FIG. 1 is an enlarged cross-sectional representation of an image intensifier tube;

FIG. 2 is a block diagram representation of an intensified video camera system suitable for use in a low cost CCTV system; FIG. 3 shows a partially cut away front view of an image intensifier tube and lens assembly;

FIG. 4 shows a side sectional view (section A-A) of the image intensifier tube and lens assembly shown in FIG. 3 coupled to an objective lens assembly and a standard video camera;

FIG. 5 is a block diagram representation of a control system for the image intensifier camera shown in FIGS. 3 and 4;

FIG. 6 shows a side sectional view (section A-A) of an alternative embodiment of the image intensifier tube and lens assembly shown in FIG. 3;

FIG. 7 is a block diagram of another embodiment of the camera system, showing the daytime operating mode;

FIG. 8 is block diagram of the camera system of FIG. 7, showing the nighttime operating mode; FIG. 9 is a cross-sectional view of an example of the camera system of FIGS. 7 and 8, showing the daytime mode;

FIG. 10 is a cross-sectional view of the camera system of FIG. 9, showing the nighttime mode;

FIG. 11 is a block diagram of a control circuit for the camera system of FIGS. 7-10;

FIGS. 12A and 12B are schematic representations of a preferred technique for rotating the image sensor assembly;

FIG. 13 is a block diagram of a further embodiment of the camera system, showing the daytime operating mode; FIG. 14 is a block diagram of the camera system of FIG. 13, showing the nighttime operating mode;

FIG. 15 is a block diagram of still another embodiment of the camera system, showing the daytime operating mode; and

FIG. 16 is a block diagram of the camera system of FIG. 15, showing the nighttime operating mode. Detailed Description

Referring now to FIG. 1 , a cross section of an image intensifier tube 10 is depicted and includes: an input glass window 11 , a photocathode 12 bonded to the surface of the input window, a microchannel plate 13 spaced apart from the photocathode, a phosphor screen 14 bonded to a glass output window 15 on the inner surface adjacent to the microchannel plate 13. Glass windows 11 and 15 also act as faceplates to the tubular housing 16 sealing the interior components 12, 13 and 14 in a vacuum. Housing 16 is preferably a solid ceramic body, although glass or other insulator materials could be used. Photocathode 12 may optionally be deposited onto the surface of input window 11. Greater detail regarding this intensifier tube may be found in a copending, commonly owned application in the names of Johnson, Scott and Bartz assigned Serial No. 08/063,234, filed May 18, 1993 and entitled "A Microchannel Image Intensifier Tube."

All of the numerical dimensions and values that follow should be taken as nominal values rather than absolutes or as a limitation on the scope of the invention. These nominal values are examples only. Many variations in size, shape and types of materials may be used, as will readily be appreciated by one skilled in the art, as successfully as the values, dimensions and types of materials specifically set forth hereinafter. In this regard, where ranges are provided, these should only be understood as guides to the practice of this invention.

FIG. 2 shows a block diagram of a video camera system 50 suitable for use in a low cost CCTV system capable of operating under all environmental lighting conditions without additional external illumination. Operationally, light 59 enters through the camera system 50 through an automatic-iris camera objective lens assembly 60. This assembly 60 controls the amount of light allowed to pass to image intensifier tube 61 , which may, for example, comprise the tube shown in FIG. 1. Power supply 62 is a high-voltage power supply for supplying the proper voltages to tube 61. In the preferred embodiment, the voltage requirements are for fixed voltages applied to various points in the tube as previously described. The output light is optically focused by relay lens 63 on the input of a CCD camera 64. A feedback signal, proportional to the intensity of the light into camera 64, is applied through lead 65 to control the auto iris lens assembly 60. The video image outputted on lead 70 may be viewed on a CCTV monitor 72.

A principal advantage of the system depicted in FIG. 2 is the modular approach in use. By using components that can be easily coupled together, such as by means of screw-on interface couplings, fabrication costs and repair and replacement costs can be dramatically reduced. The design choice of a glass output window on intensifier tube 61 and a relay lens 63 to focus the output on the input of camera 64, permits all of the components to be readily coupled together or uncoupled for replacement of the tube, camera or other components. Prior art systems couple the image intensifier tube output directly to the CCD of camera 64 via a fiber optic image conduit that is bonded and sealed in a vacuum to the CCD camera input. Not only is this prior art (CCD wafer-to-fiber optic bundle) interface expensive to make, it is impossible for a customer/user to replace the camera 64 or the intensifier tube 61 if something goes wrong with either component without replacing the entire system. The system depicted in FIG. 2 does not have this disadvantage. Notwithstanding this advantage, it is recognized that, even though the glass output window has only about one-half the throughput compared to its fiber optic equivalent and that the fiber optic equivalent has better optical resolution capability since much of the light exiting 10 the phosphor screen of intensifier tube 61 is lost and cannot be focused onto the CCD camera input, one achieves approximately the same or better optical performance as a totally sealed system by using an intensifier tube that has high gain and a high signal-to-noise ratio (such as the one depicted in FIG. 1 ). In any case, the video camera system 50 is a lower cost alternative to the prior art systems for the reasons mentioned and even with the losses, if a Gen III tube is used in the system, operation even on dark nights is more than fully satisfactory.

FIG. 3 depicts a partially cut-away front view of a structural housing for an image intensifier tube and relay lens assembly. FIG. 3 should be read in conjunction with FIG. 4 which depicts a side sectional view, taken along line A-A in FIG. 3.

Aa will be seen, the structure depicted in FIGS. 3 and 4 comprises a CCTV camera "attachment" that converts a normal daylight video camera to a day/night camera. As depicted in FIG. 4, the auto iris lens 60 and the CCD camera 64 connect to the intensifier tube 61 and relay lens 63, respectively, via a connecting means such as a standard

"C-mount" screw thread arrangement available on all commercial video products. Therefore, to convert a normal video camera to one having 24-hour viewing capability, what is required is to remove the standard auto iris lens from the camera, connect the "attachment" to the camera and then replace the auto iris lens at the input 58 shown in FIG. 4. The power connection from this attachment is to a power source which may comprise battery power as is used to power the camera. Alternatively, 24Vac or 12Vdc, commonly available power sources for CCTV installations, can be used as the power source for the attachment. Referring again to FIG. 3 and FIG. 4, housing 80 provides the structural support for the following components: image intensifier tube 61 , an optical path length compensator (OPLC) 67, each of which is mounted on a rotatable disc 101 within housing 80 along with a high-voltage power supply 62. The high-voltage power supply 62 may be mounted on disc 101 , as shown by the semi-circle outline 220 (FIG. 5). This design feature avoids moving, during rotation of disc 101 , the several high voltage leads that power image intensifier tube 61. Position sensors 81 and 82 provide electrical output signals to indicate the position of disc 101 at all times. In the configuration shown in FIGS. 3 and 4, auto iris lens 60 screws onto opening 58 which is optically aligned with the input window of the image intensifier tube 61. As stated earlier, screw threads 73 may be part of a standard C-mount to accept the male threaded auto iris lens. Similarly, CCD camera 64 screws onto the threaded opening 74 to be aligned with, in this embodiment, relay lens 63. (Both the auto iris lens 60 and the CCD camera 64 may for example be "C-mounted," to housing 80 for ease of replacement.) Electronics shown as block 79 are contained in housing 80 to control the automatic switching and rotation from nighttime low light operation to daytime high light operation. In some embodiments, it is desirable to manually control the switching from daytime to nighttime operation and in such case the automatic system 79 is either disabled or dispensed with in the system.

One of the principal advantages of this design is the rotatable disc feature that allows the image intensifier tube 61 to be inactivated and physically replaced in the through optical path by an OPLC 67 having the same optical path length as the image intensifier 20 tube. Disc 101 rotates to permit either image intensifier tube 61 (the normal nighttime configuration) or OPLC 67 (the normal daytime configuration) to be in the optical path. Turning the image intensifier tube 61 off during daylight operation not only increases the operating lifetime by reducing the on time to about 50%, but it also makes it possible to use a much less expensive auto iris lens 60, since the auto iris lens only needs to have an operational range of 104 |Uχ, as opposed to 108 lux that would otherwise be required. Switching from a nighttime configuration to a daytime configuration may be performed automatically and initiated by either a photosensor 225 (FIG. 5) or by feedback control signal via lead 65 from video camera 64. Motor 68 (FIG. 4) in combination with a gear drive assembly 69 provides the drive mechanism to move gear teeth 66 and thus disc 101 about a rotatable pivot shaft 99. As shown in FIG. 3, a simple 90 ° rotation of disc 101 moves either the image intensifier tube 61 or OPLC 67 into the optical path.

Although there are image intensifier systems having means to deactivate the image intensifier tube during daylight operation, such as those found in rifle sites, none is known to have a common optical path for both daylight and nighttime operation with means to deactivate the intensifier tube. Most systems use two separate optical channels operating as two independent systems. A reason for this may be the design problems inherent in physically removing the image intensifier tube from the optical path. A problem that must be addressed is how to replace the optical gap left, albeit small, when the image tube is physically removed from the optical path. (The image intensifier tube creates an optical image gap between the photocathode 12 in FIG. 1 and the phosphor screen 14, and the glass faceplates 11 and 15 have an index of refraction >1 that also must be taken into consideration if removed from the optical path.) The focal plane of the auto iris objective lens 60 is at the surface of the photocathode 12 in FIG. 1 ; whereas, the focal plane of the relay lens 63 is at the surface of the phosphor screen 14. In the preferred embodiment of image tube 61 , this separation is about 0.055" (1.4mm). A solution that provides poor results is to move inward either the auto iris objective lens 60 or the relay lens 63 when the image tube is removed. Moving the relay lens results in a change in the magnification of the image; whereas, moving the objective lens adds undue mechanical complications. Thus in the preferred embodiment, the OPLC 67 has an effective path length of about 0.225". If a glass plate is used, a 0.551 thick plate will properly match the image tube's effective optical path length.

The electrical control system depicted in FIG. 5 is illustrative of many different ways for controlling the rotation of disc 101 to replace the image intensifier tube 61 with an optical path length compensator 67 and vice versa. Specific examples as used in this preferred embodiment are set forth. However, as will be apparent to one skilled in the art, these may vary considerably in achieving the objectives of this invention. Referring to FIG. 5, input power (%24Vac) is applied to a standard regulated power supply 212 that provides a regulated %12Vdc to the active components in the image intensifier assembly 100 (FIG. 3). A +12V output is conducted on lead 215 to the high voltage power supply 220 via relay switch 231. Relay switch 231 interrupts the input power to the high voltage power supply 220 when the image tube 61 is removed from the optical path, and enables the same high voltage power supply when the image tube 61 is inserted back into the optical path. There are two ways shown in FIG. 5 for determining when to interchange image tube 61 for fiber optic image conduit 67. As will be explained, either the feedback control signal on lead 65 or alternatively an independent photosensor and amplifier 225, if activated, initiate the switching of image tube 61 with OPLC 67. Incoming (ambient) light enters the auto iris lens 60 and is either amplified or passed through to the relay lens 63 (FIG. 4), depending upon whether image tube 61 or OPLC 67 is in the optical path. The light image is then picked up by video camera 64. Operationally, when the light at the input to video camera 64 drops below 0.1 lux, image tube 61 is activated and inserted into the optical path. The feedback control signal on lead 65 is applied, via video signal amplifier 229, to a day/night comparator circuit 228. When the level of the video control signal on lead 65 drops below a predetermined level indicating that the iris is fully open and the ambient light is below the 0.1 lux needed for acceptable video monitoring, comparator 228 signals the set/reset control circuit 226 to switch to image tube 61. At that point, the set/reset control circuit 226 takes control of the auto iris 60 by closing down the iris via control switch 227. Control circuit 226 also initiates the substitution of image tube 61 for OPLC 67 by sending a "set" signal to direction control circuit 230. Direction control circuit 230 energizes motor 68, causing disc 101 to rotate to place image tube 61 in the optical path. Limit switch 82 senses when disc 101 is in the proper position for the image tube to operate, causing direction control circuit 230 to deactivate motor 68. Once image tube 61 is operational (after a timed interval), control circuit 226 releases control of the auto iris control switch 227 permitting the auto iris 60 to again be proportionally controlled by the video control signal on lead 65. The actual change from fiber optic plate 67 to image tube 61 , or vice versa, takes about one second in the preferred embodiment. During this change over period, the circuit seizes control of the auto iris lens 60 to close down the iris lens and protect image tube 61 from potential burn out. In the transition from night to day when the iris lens closes down fully to restrict the incoming light, the level of the video control signal on lead 65 increases above a predetermined level indicating that the iris lens is closed and the ambient light is above the 0.1 lux needed for acceptable video monitoring. Then the process basically repeats itself, substituting the OPLC 67 for image tube 61. In the previously discussed image enhancement system depicted in FIGS. 3 and 4, the image intensifier tube may be physically replaced in the optical path by a fiber optic image conduit or other optical path length compensator 67 through a rotation of disc 101. Alternately, the image intensifier tube 61 may be physically replaced during periods of daytime lighting by a second relay lens. FIG. 6 depicts a partially cut-away front view of an alternate structural housing for an image intensifier tube and a second relay lens 84 as part of rotatable disc 101. In this embodiment, relay lens 83 that operates in conjunction with the image intensifier tube 61 is supported, not by the housing 80, but by an added flange on disc 101. Although the focal planes remain the same as the other structural embodiment, lens 83 rotates out of the optical path with the image intensi¬ fier tube 61. A second relay lens 84 moves into the optical path position vacated by the image intensifier tube 61 and the first relay lens 83. By being able to replace the combined tube and lens structure 61 and 83, a second lens can be designed to have basically the same functional performance as the OPLC 67 depicted in FIG. 4. The main design criteria is to have the focal plane of the auto iris objective lens 60 match the focal plane of the second relay lens 84.

Some of the benefits of the previously discussed image enhancement systems can be achieved with portions of the system illustrated in FIG. 2. A lens 57 shown in FIG. 2 which may for example be a telephoto lens, is attached to the front end of auto iris lens 60 in line with an intensifier tube (and without the other elements of FIG. 2) provides a simple and inexpensive day/night system. This is particularly the case when standard C-mount couplings are used. In such an embodiment, one relies on the iris to reduce the daytime input and the intensifier to increase the nighttime viewing. In this case, the image intensifier does not get turned off, and thus this embodiment does not obtain the many advantages of the preferred embodiments. However, it offers a very simple and inexpensive solution to day/night surveillance.

The camera system FIGS. 3-5 and described above provides highly satisfactory results for both daytime and nighttime operation. However, the optical path length compensator causes some degradation of the resolution of the image that is formed on the CCD sensor during daytime operation. The degraded resolution occurs because of the structure of the diffuser of the OPLC. In addition, the optical path length compensator reduces the light level received by the CCD sensor because some of the diffused light rays are not collected by the relay lens. The result is that the daytime image is not as clear and bright as is the case when the CCD camera is directly connected to the input lens. A block diagram of a camera system which provides high quality images for both daytime and nighttime operation is shown in FIGS. 7 and 8, which illustrate daytime and nighttime configurations, respectively. The embodiment of FIGS. 7 and 8 preferably uses a CCTV video camera having an image sensor that is separate from an electronics assembly. As shown in FIGS. 7 and 8, a CCTV camera 300 includes an image sensor assembly 302 and an electronics assembly 304 interconnected by a cable 306, such as a ribbon cable. The image sensor assembly 302 includes an image sensor, such as a CCD sensor 308. An example of a suitable CCTV camera 300 is the Model IK-M40A Microminiature Color CCD Camera sold by Toshiba. The camera system further includes an input lens 310, typically an auto iris lens, and an image intensifier assembly 312. The image intensifier assembly 312 is mounted on a disk 314 for rotation about an axis 316. The image intensifier 312 includes an image intensifier tube assembly 320 and a relay lens 322 for transferring an image from screen of the image intensifier tube 320 to the CCD sensor 308 in the nighttime mode, as shown in FIG. 8. The image intensifier assembly 312 may further include an expander lens 324 as discussed below.

The configuration used in the daytime mode is shown in FIG. 7. The image sensor assembly 302 is positioned on an optical axis 328 directly behind input lens 310 so as to receive an image directly from input lens 310. In the daytime mode, no optical element which could degrade resolution or reduce light level is positioned between the input lens 310 and the image sensor assembly 302. Thus, the camera 300 produces a high quality daytime image. In the daytime mode, image intensifier assembly 312 is removed from optical axis 328 and does not function. Typically, the image intensifier tube 320 is deenergized in the daytime mode to extend its operating life.

The configuration used in the nighttime mode is shown in FIG. 8. The image intensifier assembly 312 is positioned on optical axis 328 between input lens 310 and image sensor assembly 302. The image sensor assembly 302 is positioned on optical axis 328 but has been moved backward along axis 328 to a position directly behind the image intensifier assembly 312. The image intensifier tube 320 receives an image from input lens 310 and forms an intensified image on its output screen. The intensified image is transferred by relay lens 322 to the image sensor assembly 302. As a result, the camera 300 produces a bright, high quality image during nighttime operation without requiring additional illumination of the area being observed.

It can be seen that both the image sensor assembly 302 and the image intensifier assembly 312 are moved when switching between the daytime mode and the nighttime mode. The image intensifier assembly 312 is moved onto the optical axis 328 in the nighttime mode and is removed from the optical axis 328 in the daytime mode, typically by rotation of disk 314 about axis 316 as described below. The image sensor assembly 302 is moved forward and backward along optical axis 328 between daytime and nighttime positions, typically by a linear drive mechanism as described below. The image sensor assembly 302 is moved along optical axis 328 through an opening 378 in disk 314. In addition, the image sensor assembly 302 is preferably rotated by 180 ° between the daytime configuration shown in FIG. 7 and the nighttime configuration shown in FIG. 8. The 180 ° rotation compensates for an image inversion produced by image intensifier assembly 312 and, more specifically, by relay lens 322. Alternatively, the image inversion can be effected electronically. In this case, rotation of the image sensor assembly 302 is not required.

The image intensifier tube 320 can be of the type shown in FIG. 1 and described above. The input lens 310, typically an auto iris lens that is compatible with camera 300, focuses an image on the cathode of the image intensifier tube 320. The intensified image formed on the screen of the image intensifier tube 320 is transferred by relay lens 322 to the CCD sensor 308 in the image sensor assembly 302.

The expander lens 324 is utilized in the example of FIGS. 7 and 8 because the CCD sensor 308 in image sensor assembly 302 and input lens 310 typically have a one-half inch format, whereas the image intensifier tube 320 typically has a one inch format. The expander lens 324 expands the image formed by input lens 310 to a one inch format at image intensifier tube 320. The one inch format image at the output of image intensifier tube 320 is converted by relay lens 322 to the one-half inch format of the CCD sensor 308 in image sensor assembly

302. This configuration avoids any loss in resolution resulting from failure to use the entire area of the image intensifier tube 320. It will be understood that the expander lens 324 is not required in situations where the input lens 310, the image intensifier tube 320 and the CCD chip all have the same image format.

A preferred embodiment of the camera system of FIGS. 7 and 8 is shown in FIGS. 9 and 10. The configuration used in the daytime mode is shown in FIG. 9, and the configuration used in the nighttime mode is shown in FIG. 10. The image sensor assembly 302 is mounted for linear movement along optical axis 328 and for rotation by 180 ° between the positions shown in FIGS. 9 and 10. The image sensor assembly 302 is supported by a cylindrical flange 338 mounted to a housing member 340. The flange 338 is fixed in position but permits sliding movement of image sensor assembly 302. The image sensor assembly 302 is also supported by a movable support member 342. A bearing 344 secured in support member 342 permits rotation of image sensor assembly 302 about optical axis 328 relative to support member 342. The support member 342 is movably mounted to a ball screw 348 by a ball nut 346 affixed to support member 342. The ball screw 348 is supported by a bearing 355 mounted to housing member 340 and a bearing 356 mounted to a housing member 357. The ball screw 348 is mechanically coupled by gears 350 and 352 to a motor 354. When the motor 354 is energized, the ball screw 348 rotates, causing linear movement of support member 342 and image sensor assembly 302 along optical axis 328. The CCD sensor 308 mounted in image sensor assembly 302 is thus moved by motor 354 between the daytime position shown in FIG. 9 and the nighttime position shown in FIG. 10. Limit sensors 410 (FIG. 11 ), such as photosensors, are preferably used to deenergize the motor 354 at each end of its travel. As noted above, the CCD sensor 308 is preferably rotated by

180 ° between daytime and nighttime positions to compensate for image inversion by the image intensifier tube 320. As shown in FIGS. 12A and 12B, the rotation of CCD sensor 308 may be effected by a pin 360 extending inwardly from flange 338 and a helical groove 362 in the housing of image sensor assembly 302. The image sensor assembly 302 is free to rotate by at least 180 ° within support member 342. The pin 360 secured to flange 338 engages the groove 362 in the housing of the image sensor assembly 302. As the image sensor assembly 302 is moved linearly by motor 354, the pin 360 follows the groove 362, causing the image sensor assembly 302 to be rotated through the desired angle. It will be understood that the mechanical arrangement shown in FIGS. 9, 10, 12A and 12B for effecting linear and rotational movement of image sensor assembly 302 is but one example of a suitable configuration and that other configurations are included within the scope of the present invention.

As best shown in FIG. 10, the image intensifier assembly 312 is mounted in disk 314. The disk 314 is supported by a shaft 370 for rotation about axis 316. The disk 314 is mechanically coupled through gears 372 and 374 to a motor 376. When the motor 376 is energized, the disk 314 is caused to rotate about axis 316 between a nighttime position as shown in FIG. 10 and a daytime position as shown in FIG. 9. In the nighttime position, the image intensifier assembly 312 is rotated into alignment with optical axis 328 between input lens 310 and image sensor assembly 302. In the daytime position, the image intensifier assembly 312 is removed from the optical axis 328, and the disk 314 is rotated such that the opening 378 in disk 314 is aligned with the optical axis 328, thereby permitting the image sensor assembly 302 to be moved forward to the daytime position shown in FIG. 9. It will be understood that the image sensor assembly 302 can be moved forward to the daytime position only after the disk 314 has been rotated to the daytime position as shown in FIG. 9. Limit sensors 402 (FIG. 11 ), such as photosensors, can be utilized to deenergize motor 376 at each end of its travel. It will be understood that the configuration shown in FIGS. 9 and 10 for moving the image intensifier assembly 312 into and out of the optical axis 328 is but one example of a suitable arrangement and that other configurations are included within the scope of the present invention.

A control circuit for the camera system of FIGS. 7-10 is shown in FIG. 11. The motor 376 which rotates the disk 314 is controlled by a motor controller 400. The motor controller 400 receives control inputs from limit sensors 402 and from a day/night decision and control unit 404. The motor 354 which translates the CCD sensor 308 along optical axis 328 is controlled by a motor controller 406. The motor controller 406 receives control inputs from limit sensors 410 and from the day/night decision and control unit 404.

The control unit 404 receives on a line 412 a day/night control signal which represents daytime or nighttime, in response to a sensed ambient light level. When the signal on line 412 represents a transition from daytime to nighttime, the control unit 404 first causes motor 354 to be energized so that the image sensor assembly 302 is translated from the daytime position as shown in FIG. 9 to the nighttime position as shown in FIG. 10. Then the control unit 404 causes the motor 376 to be energized so that the image intensifier assembly 312 is rotated into the optical axis 328 as shown in FIG. 10. The limit sensors 402 and 410 sense the limits of travel of the disk 314 and the image sensor assembly 302, respectively, and cause the motors 376 and 354 to be deenergized. When the camera system is switched into the nighttime mode, the control unit 404 causes an intensifier switch 414 to energize an intensifier high voltage power supply 416 which supplies power to image intensifier tube 320. Thus, the image intensifier tube 320 is energized during the nighttime mode.

When the signal on line 412 represents a transition from nighttime to daytime, a reverse of the above sequence occurs. The motor 376 is energized, causing the image intensifier assembly 312 to be rotated out of the optical axis 328. Then, the motor 354 is energized, causing the image sensor assembly 302 to be translated forwardly along optical axis 328 to the daytime position as shown in FIG. 9. During the daytime mode, the intensifier high voltage power supply 416 is preferably deenergized, thus extending the operating life of the image intensifier tube. The day/night control signal on line 412 can be obtained from one of two sources. A photodiode 420 can be used to sense the ambient light level. The photodiode output is supplied through a photosensor amplifier 422 to a comparator 424, which may have an adjustable reference level. The reference level establishes the corresponding light level at which the transition between daytime and nighttime operating modes occurs. The output of comparator 424 is supplied to a mode select switch 426. Alternatively, the day/night control signal can be derived from an auto iris lens control signal. It will be understood that the CCTV camera 300 typically supplies a control signal to auto iris lens 310 to provide a more or less constant input light level to the camera. Thus, the auto iris control signal represents ambient light level. A video signal representative of the auto iris control signal is supplied from a lens closing circuit 430 through a video amplifier 432 to a comparator 434. The comparator 434 preferably has an adjustable reference level, which establishes a corresponding light level for the transition between daytime and nighttime modes. The output of comparator 434 is supplied to mode select switch 426. The mode select switch 426 permits either source of the day/night control signal to be selected. The day/night control signal from the selected source is supplied on line 412 to control unit 404.

The lens closing circuit 430 is interposed in the auto iris control signal supplied by the camera 300 to the auto iris lens 310. During transitions between daytime and nighttime modes and between nighttime and daytime modes, the auto iris lens 310 is fully closed to prevent high ambient light levels from reaching the image intensifier tube 320 and the CCD sensor 308. A power supply 434 converts 24 volt AC input to 12 volts DC. The DC voltage is supplied to the motors 354 and 376, the intensifier high voltage power supply 416 and the control circuitry. It will be understood that the control circuit shown in FIG. 11 is but one example of a suitable circuit and that other control circuits are included within the scope of the present invention.

The camera system shown in FIGS. 7-11 and described above may utilize a black and white or color camera 300. The high resolution and high sensitivity of the black and white camera provides not only high resolution daytime operation, and operation in twilight conditions before the image intensifier assembly is switched into the optical path, but also provides high sensitivity nighttime operation down to the darkest of nights, and provides nighttime resolution in excess of 450 lines. However, the embodiment shown in FIGS. 7-11 does not fully solve the problem of the low sensitivity and low resolution of the color CCD camera.

Color CCD cameras have poorer resolution and less sensitivity than black and white CCD cameras because the color cameras have three color sensors at each pixel location. Typically, a color camera has 450 lines of resolution, as compared with 650 lines of resolution for the black and white camera, and has a sensitivity for full video of a few lux, as compared with a few tenths of a lux for a black and white camera. The color daytime image is therefore poorer than the black and white daytime image.

A more significant problem with the color CCD camera occurs when it is coupled with an image intensifier for nighttime operation. The resolution of the combination of the image intensifier and the CCD camera is determined by the product of the modulation transfer functions of the camera and the image intensifier. When a black and white CCD camera is used with the image intensifier, total system resolution of 500 lines can be achieved, whereas only 350 lines can be obtained when the color CCD camera is used. The sensitivity problem is worse than the resolution problem. Since the sensitivity of the color camera is about 1/10 the sensitivity of the black and white camera, the combination of image intensifier and color camera does not work at the lowest light levels that occur on moonless nights. Also with the auto iris lens adjusted to give a good resolution picture without scintillation noise, the light level on the faceplate of the image intensifier tube will be ten times higher when the color camera is used than when the black and white camera is used, and this will reduce the intensifier tube life by an order of magnitude.

An embodiment of the camera system of the present invention which overcomes these problems and provides optimum color daytime performance and good high resolution, long life, nighttime operation is shown in FIGS. 13 and 14. Like elements in FIGS. 7, 8, 13 and 14 have the same reference numerals. The camera system of FIGS. 13 and 14 uses a color camera for daytime operation and a black and white camera for nighttime operation. Each camera has an image sensor assembly that is separate from an electronics assembly. The image sensor assembly and the electronics assembly are connected by a cable, such as a ribbon cable.

FIGS. 13 and 14 illustrate daytime and nighttime configurations, respectively. A color CCTV camera 500 includes a color image sensor assembly 502 and a color camera electronics assembly 504 interconnected by a cable 506. The image sensor assembly 502 includes a black and white image sensor, such as a CCD sensor. The color image sensor assembly 502 is mounted on disk 314. The camera system further comprises an image intensified camera assembly, including a black and white CCTV camera 510, image intensifier tube 320 and relay lens 322, and may include expander lens 324. The black and white CCTV camera 510 includes a black and white image sensor assembly 512 and a black and white camera electronics assembly 514 interconnected by a cable 516. The image sensor assembly 512 includes a black and white image sensor, such as a CCD sensor. Expander lens 324, image intensifier tube 320, relay lens 322 and black and white image sensor assembly 512 are mounted on disk 314 in optical alignment with each other. The camera system further includes input lens 310, typically an auto iris lens. The disk 314 is mounted for rotation about axis 316 so that either image sensor assembly 502 or the assembly comprising expander lens 324, image intensifier tube 320, relay lens 322 and image sensor assembly 512 is brought into alignment with input lens 310. In FIGS. 13 and 14, the image sensor assembly 502 is shown on the opposite side of disk 314 from expander lens 324, image intensifier tube 320, relay lens 322 and image sensor assembly 512. It will be understood that these elements can be separated on disk 314 by any angle that is permitted by the mechanical configurations of these elements. For example, in FIG. 3, the disk 101 rotates through about 90 ° .

The configuration used in the daytime mode is shown in FIG. 13. The color image sensor assembly 502 is positioned on optical axis 520 directly behind input lens 310 so as to receive an image directly from input lens 310. In the daytime mode, no optical element which could degrade resolution or reduce light level is positioned between the input lens 310 and the color image sensor assembly 502. Thus, the camera 500 produces a high quality daytime color image. In the daytime mode, the expander lens 324, the image intensifier tube 320, the relay lens 322 and the black and white image sensor assembly 512 are rotated out of the optical axis 520 and do not function. Typically the image intensifier tube 320 and the black and white camera 510 are deenergized in the daytime mode.

The configuration used in the nighttime mode is shown in FIG. 14. The portion of the image intensified camera assembly including expander lens 324, image intensifier tube 320, relay lens 322 and black and white image sensor assembly 512 is positioned on optical axis 520 in alignment with input lens 310. The image intensifier tube

320 receives an image from input lens 310 and forms an intensified image on its output screen. The intensified image is transferred by relay lens 322 to the black and white image sensor assembly 512. As a result, the black and white camera 512 produces a bright, high quality image during nighttime operation without requiring additional illumination of the area being observed. The expander lens 324 expands the image from the 1/2 inch format of the input lens 310 to the one inch format of the image intensifier tube 320, as described above.

During nighttime operation, the color CCTV camera 500 is deenergized. The color image sensor assembly 502 is rotated out of the optical axis 520 in the nighttime mode.

The disk 314 can be rotated between the daytime position shown in FIG. 13 and the nighttime position shown in FIG. 14 by a drive assembly similar to that shown in FIGS. 3 and 4, with suitable modification of the disk 314 to accommodate the elements shown in FIGS. 13 and 14. The control system for the configuration shown in FIGS. 13 and 14 can be similar to the control system shown in FIG. 5 and described above. In addition, the day/night control signal is used to deenergize the black and white CCTV camera 510 during daytime operation and is used to deenergize color CCTV camera 500 during nighttime operation. Furthermore, the day/night control signal is used to control a switch 524 which receives video signals from the color camera electronics assembly 504 and the black and white camera electronics assembly 514. During daytime operation, the switch 524 supplies video from the color camera 500 to a monitor. During nighttime operation, the switch 524 supplies video from the black and white camera 510 to the monitor. A further embodiment of the camera system of the present invention is shown in FIGS. 15 and 16. The embodiment of FIGS. 15 and 16 is similar to the embodiment of FIGS. 13 and 14, but typically provides a black and white image in both daytime and nighttime modes and provides a cost reduction as compared with the embodiment of FIGS. 13 and 14. Like elements in FIGS. 13-16 have the same reference numerals. The camera system of FIGS. 15 and 16 uses a video camera, typically a black and white CCTV camera, having two image sensor assemblies and a single electronics assembly. As described below, one of the image sensor assemblies is used in the daytime mode, and the other is used in the nighttime mode.

FIGS. 15 and 16 illustrate daytime and nighttime configurations, respectively. A CCTV camera 600 includes a camera electronics assembly 602 selectively connected by a switch 604 to an image sensor assembly 606 or to an image sensor assembly 608. The switch 604 is controlled by the day/night control signal described above. The image sensor assembly 606 is connected by a cable 610 to switch 604, and image sensor assembly 608 is connected by a cable 612 to switch 604. The image sensor assemblies 606 and 608 include image sensors, such as CCD sensors. The image sensor assembly 606 is mounted on disk 314. The camera system further comprises an image intensifier assembly 620, including image intensifier tube 320, relay lens 322 and image sensor assembly 608, and may include expander lens 324. The expander lens 324, image intensifier tube 320, relay lens 322 and image sensor assembly 608 are mounted on disk 314 in optical alignment with each other. The disk 314 is mounted for rotation about axis 316 so that either the image sensor assembly 606 or the image intensifier assembly 620 is brought into alignment with input lens 310.

The configuration used in the daytime mode is shown in FIG. 15. The image sensor assembly 606 is positioned on optical axis 520 directly behind input lens 310 so as to receive an image directly from input lens 310 without any intervening optical elements. The switch 604 couples the image sensor assembly 606 to camera electronics assembly 602 to produce a high quality daytime image. In the daytime mode, the image intensifier assembly 620 is rotated out of the optical axis 520 and does not function. Typically, the image intensifier tube 320 is deenergized in the daytime mode.

The configuration used in the nighttime mode is shown in FIG. 16. The image intensifier assembly 620 is positioned on optical axis 520 in alignment with input lens 310. The image intensifier tube 320 receives an image from input lens 310 and forms an intensified image on its output screen. The intensified image is transferred by relay lens 322 to the image sensor assembly 608. The switch 604 couples image sensor assembly 608 to camera electronics assembly 602 to provide a bright, high quality image during nighttime operation without requiring additional illumination of the area being observed. The image sensor assembly 606 is rotated out of the optical axis 520 in the nighttime mode.

While there have been shown and described what are at present considered the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS What is claimed is:
1. A camera system for operation in daytime and nighttime lighting conditions without additional illumination, comprising: a video camera having an image sensor; an image intensifier assembly including an image intensifier tube; an input lens for receiving incoming light representative of an image; and a controller for switching between a nighttime mode wherein said image intensifier assembly is positioned on an optical axis between said input lens and said image sensor, and said image sensor is positioned to receive an image from said image intensifier assembly, and a daytime mode wherein said image intensifier assembly is removed from said optical axis and said image sensor is positioned along said optical axis to receive an image directly from said input lens.
2. A camera system as defined in claim 1 wherein said controller comprises, first means for moving said image intensifier assembly between a nighttime position on said optical axis and a daytime position removed from said optical axis; and second means for moving said image sensor forward and backward along said optical axis between a nighttime position for receiving an image from said image intensifier assembly and a daytime position for receiving an image directly from said input lens.
3. A camera system as defined in claim 2 wherein said first means comprises means for rotating said image intensifier assembly between said daytime and nighttime positions.
4. A camera system as defined in claim 2 wherein said second means comprises means for translating said image sensor along said optical axis between said daytime and nighttime positions.
5. A camera system as defined in claim 1 wherein said image intensifier assembly further includes a relay lens for transferring said image from said image intensifier tube to said image sensor in said nighttime operating mode.
6. A camera system as defined in claim 5 wherein said image intensifier assembly further includes an expander lens for expanding an image formed by said input lens to match an image format of said image intensifier tube.
7. A camera system as defined in claim 2 wherein said controller further comprises third means for rotating said image sensor by 180 ° between said daytime and nighttime positions to compensate for image inversion by said image intensifier assembly.
8. A camera system as defined in claim 1 wherein further including means for sensing an ambient light level, said controller including means responsive to said ambient light level for automatically switching to and between said nighttime mode and said daytime mode.
9. A camera system as defined in claim 2 wherein said first means comprises a disk for mounting said image intensifier assembly and a motor for rotating said disk between said daytime and nighttime positions.
10. A camera system as defined in claim 9 wherein said second means includes a support for said image sensor and a linear drive for moving said support between said daytime and nighttime positions.
1 1. A camera system as defined in claim 1 wherein said image sensor comprises a charge coupled device (CCD) sensor.
12. A camera system as defined in claim 2 wherein said video camera comprises an image sensor assembly containing said image sensor, and an electronics assembly separate from said image sensor assembly and connected thereto by a cable, said image sensor assembly being movable along said optical axis.
13. A camera system as defined in claim 1 wherein said input lens comprises an auto iris lens that is controlled by said video camera.
14. A method for performing surveillance in daytime and nighttime lighting conditions without additional illumination, comprising the steps of: providing a video camera including an image sensor, an image intensifier assembly and an input lens for receiving incoming light representative of an image; and switching between a nighttime mode wherein said image intensifier assembly is positioned on an optical axis between said input lens and said image sensor, and said image sensor is positioned to receive an image from said image intensifier assembly, and a daytime mode wherein said image intensifier assembly is removed from said optical axis and said image sensor is positioned along said optical axis to receive an image directly from said input lens.
15. A method for performing surveillance as defined in claim 14 wherein the step of switching between a nighttime mode and a daytime mode includes: moving said image intensifier assembly between a nighttime position on said optical axis and a daytime position removed from said optical axis, and moving said image sensor forward and backward along said optical axis between a nighttime position for receiving an image from said image intensifier assembly and a daytime position for receiving an image directly from said input lens.
16. A method for performing surveillance as defined in claim 15 wherein the step of switching between a nighttime mode and a daytime mode further includes rotating the image sensor by 180 ° between the daytime and nighttime positions to compensate for image inversion by the image intensifier assembly.
17. A method for performing surveillance as defined in claim 14 further including the step of sensing an ambient light level, the step of switching between nighttime mode and a daytime mode including automatically switching to and between the nighttime and daytime modes in response to said ambient light level.
18. A camera system for operation in daytime and nighttime lighting conditions without additional illumination, comprising: an input lens for receiving incoming light representative of an image, said input lens having an optical axis; a first video camera having a first image sensor; an image intensified camera assembly including an image intensifier tube and a second video camera having a second image sensor, said second image sensor being positioned to receive an intensified image from said image intensifier tube; and a controller for switching between a nighttime mode wherein said image intensifier tube and said second image sensor are positioned on the optical axis of said input lens, and a daytime mode wherein the first image sensor of said first video camera is positioned on the optical axis of said input lens.
19. A camera system as defined in claim 18 wherein said first video camera comprises a color camera and said second video camera comprises a black and white camera.
20. A camera system as defined in claim 18 wherein said second video camera has higher resolution and sensitivity than said first video camera.
21 . A camera system as defined in claim 18 wherein said controller comprises a disk for mounting said first image sensor and for mounting said image intensifier tube and said second image sensor and means for rotating said disk between daytime and nighttime positions.
22. A camera system as defined in claim 18 wherein said image intensified camera assembly further includes a relay lens for transferring said intensified image to said second image sensor.
23. A camera system as defined in claim 18 wherein said image intensified camera assembly further includes an expander lens for expanding the image formed by said input lens to match an image format of said image intensifier tube.
24. A camera system as defined in claim 18 further including means for sensing an ambient light level, said controller including means responsive to said ambient light level for automatically switching to and between said nighttime mode and said daytime mode.
25. A camera system as defined in claim 18 wherein said first and second video cameras each comprise an image sensor assembly containing said image sensor, and an electronics assembly separate from said image sensor assembly and connected thereto by a cable.
26. A camera system as defined in claim 18 wherein said controller includes means for switching a video output of said first video camera to a monitor in the daytime mode and for switching a video output of said second video camera to the monitor in the nighttime mode.
27. A camera system for operation in daytime and nighttime lighting conditions without additional illumination, comprising: an input lens for receiving incoming light representative of an image, said input lens having an optical axis; a first image sensor; an image intensifier assembly including an image intensifier tube and a second image sensor, said second image sensor being positioned to receive an intensified image from said image intensifier tube; a camera electronics assembly; and a controller for switching between a nighttime mode wherein said image intensifier assembly is positioned on the optical axis of said input lens and said second image sensor is coupled to said camera electronics assembly, and a daytime mode wherein said first image sensor is positioned on the optical axis of said input lens and is coupled to said camera electronics assembly.
28. A camera system as defined in claim 27 wherein said controller comprises a disk for mounting said first image sensor and said image intensifier assembly, and means for rotating said disk between a daytime position wherein said first image sensor is located on said optical axis and a nighttime position wherein said image intensifier assembly is located on said optical axis.
29. A camera system as defined in claim 27 wherein said image intensifier assembly further includes a relay lens for transferring said intensified image to said second image sensor.
30. A camera system as defined in claim 29 wherein said image intensifier assembly further includes an expander lens for expanding the image formed by said input lens to match an image format of said image intensifier tube.
31 . A camera system as defined in claim 27 further including means for sensing an ambient light level, said controller including means responsive to said ambient light level for automatically switching to and between said nighttime mode and said daytime mode.
PCT/US1994/009191 1993-08-19 1994-08-12 Surveillance system with image intensifier tube WO1995005716A1 (en)

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US4646140A (en) * 1984-09-25 1987-02-24 English Electric Valve Company Limited Television cameras
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