Abstract:
A method and apparatus utilizing a series of optical components and systems which effectively detect and locate electromagnetic imaging or detection systems or devices, such as cameras and passive infrared detectors. A light source is arranged in a specially-prescribed manner, and is used in conjunction with imaging optics to illuminate an area. Any electromagnetic imaging or detection system in the illuminated area is detected with either the user&#39;s eye directly, or with detection optics to determine the existence of such electromagnetic imaging or detection system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of co-pending U.S. provisional application Ser. No. 60/125,988 entitled METHOD AND APPARATUS FOR LOCATING HIDDEN CAMERAS filed Mar. 24, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to the detection of electromagnetic imaging and/or detection systems, and more particularly to a method and apparatus for detecting and locating hidden cameras. 
     Hidden cameras are becoming commonplace. These cameras are used to observe and/or record pictures of someone else&#39;s activities without their knowledge. In most cases it&#39;s legal, and often necessary. In places such as banks, convenience stores, government facilities, and casinos, hidden cameras are used to help prevent crime and identify criminals. However, the laws of only a few states expressly prohibit the unauthorized installation or use of cameras in private places. This means that, in most states, the use of a hidden camera in a private place without the permission of the people being observed is not expressly prohibited. 
     A decade ago, covert video surveillance was not a serious problem since state-of-the-art video equipment was expensive, bulky, and difficult-to-find. Now, covert video equipment is extremely advanced, tiny, inexpensive, and ludicrously easy to find. These tiny video cameras can be hidden virtually anywhere, with an aperture of less than ⅛ inch in diameter. In fact they are commonly sold, already installed, inside such everyday items as exit signs, smoke detectors, sunglasses, picture frames, telephones, houseplants, clocks, writing pens, wristwatches, briefcases, and even teddy bears. 
     The lax video surveillance laws in most states, coupled with the increasing availability of high-quality spy cameras, make covert video surveillance a real concern for many people. Mass media coverage of hidden camera video voyeurs is on the rise. As public awareness of this issue increases, so does paranoia. People would like to feel secure that they are not being videotaped, especially in private places like their own homes and offices. 
     It is therefore an object of this invention to effectively detect and locate cameras, passive infra-red (PIR) detectors, and other electromagnetic imaging or detection systems. 
     It is another object of this invention to effect such detection and location without reliance on electronic signals emitted by the electromagnetic imaging or detection system. 
     It is still another object of this invention to perform such detection and location via an optical system which avoids problems associated with electronic or magnetic shielding. 
     It is a further object of this invention to effect such detection regardless of whether the electromagnetic imaging or detection system is on or off, is electronic in nature and/or includes auto-focussing mechanisms. 
     SUMMARY OF THE INVENTION 
     The objects set forth above as well as further and other objects and advantages of the present invention are achieved by the embodiments of the invention described hereinbelow. 
     The present invention utilizes a series of optical components and systems to detect and locate electromagnetic imaging and detection systems, such as cameras or PIR detectors, which, in many instances, are hidden. The basic concept of the present invention involves illuminating by a beam of electromagnetic radiation or energy an area in which a hidden camera is located. When this beam of electromagnetic radiation, in the form of light, for example, hits the camera lens, it is focused onto a partially-reflective imaging plane (like the CCD plane in a video camera). Some of the light is then retro-reflected back through the lens in the same direction from which it originated. In one embodiment of the invention, electromagnetic imaging and detection systems, such as hidden cameras are highlighted by continuous light such as bright red light against a green background, for easy identification by the user. In another embodiment of the invention, electromagnetic imaging and detection systems are highlighted by flashing light such as flashing red light against a non-flashing background, for easy identification by the user. In further embodiments, detection is accomplished by further and other characterizations of the beam of electromagnetic radiation and detected electronically with the use of optical sensors. Even further embodiments of the present invention provide further enhancements which include, but are not limited to, for example, scanning of the emitted beam under computer control. 
    
    
     For a better understanding of the present invention, together with other and further objects thereof, reference is made to the accompanying drawings and detailed description and its scope will be pointed out in the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of the principle involved in describing the present invention; 
     FIG. 2 is a schematic illustration of components making up the basic concept of the present invention; 
     FIG. 3 is a schematic illustration of a preferred embodiment of the present invention; 
     FIG. 4 is a schematic illustration of a front view of a portion of the preferred embodiment of the present invention shown in FIG. 3; 
     FIG. 5 is a schematic illustration of an alternative embodiment of the present invention; 
     FIG. 6 is a graphic representations of an on-off cycle for illuminators used with the present invention. 
     FIG. 7 is a schematic illustration of another preferred embodiment of the present invention; 
     FIG. 8 is a schematic circuit diagram of the electronics used in the preferred embodiment of the present invention shown in FIG. 7; 
     FIGS. 9 and 11 are graphic representations of on-off cycles for illuminators used with the present invention; 
     FIG. 10 is a schematic representation of the overlapping of beams within the present invention as shown in FIG. 7; 
     FIG. 12 is a schematic illustration of another embodiment of the present invention; 
     FIG. 13 is a schematic illustration of a further embodiment of the present invention; 
     FIG. 14 is a pictorial schematic representation of a further embodiment of the present invention; and 
     FIGS. 15-26 represent schematic illustrations of further embodiments and possible variations of the illuminator/detector systems used within the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following descriptions of the present invention, the term “electromagnetic radiation (energy)” includes, for example, light and any other forms of electromagnetic radiation (energy) with wavelength(s) in the range from 0.1 micron to 15 microns. Also, in the following description, the term “electromagnetic imaging and detection system” includes a camera or any other device or system that utilizes a focusing mechanism to detect and/or image electromagnetic radiation with wavelength(s) in the range from 0.1 micron to 15 microns. 
     The basic concept of the present invention involves illuminating an area in which a hidden camera is located. When light hits the camera lens, it is focused onto a partially-reflective imaging plane (like the CCD plane in a video camera). Some of the light is then retro-reflected back through the lens in the same direction from which it originated. FIG. 1 shows a schematic of this principle. A ray of light  10  from some outside source is incident on a target imaging system  12 . In passing through the imaging system&#39;s objective lens  14 , the light refracts  16  and is focused on an imaging plane  18 . The imaging plane  18  may be, but is not limited to, a CCD array, a microchannel plate, an image intensifier, a photodiode or array of photodiodes, a diffuse screen, or a retina, for example. In any case, the imaging plane  18  is at least partially reflective. Thus, light is then reflected  20  back out toward the objective lens  14 , and is once again refracted. The light emerges  22  from the imaging system  12  in a direction equal and opposite to the incoming light beam  10 . 
     FIG. 2 shows the basic concept of the present invention where an illumination output source  30  (which may or may not be connected, via optical and/or electronic means  32 , to control electronics and/or optics  34 ) is used in conjunction with an optical receiving means  54  (which may or may not be connected via optical and/or electronic means  56 , to control electronics and/or optics  58 ) to detect retro-reflections from a target such as a hidden imaging system  40 . The illumination output source  30  is said to be an “on-axis illuminator,” because the illumination output source  30  is “on-axis” with (or “very near”) the optical receiving means  54  thus the receiver is capable of receiving light from source  30  retro-reflected from the target. In practice, the brightness of light retro-reflected from-an imaging system  40 , such as a camera, is much greater than the brightness of light scattered from a diffuse surface (such as a white wall, for example). The reason for this is that the retro-reflected light is confined within a defined retro-reflected light zone (between ray  50  and ray  52 ) while diffusely scattered light is reflected evenly in all directions. Thus the distinction is made between “retro-reflected light”, which is confined within a narrow retro-reflected light zone, and “diffusely scattered light” or “reflected light from shiny objects”, which is scattered over a much larger reflected light zone. While diffusely scattered light and reflected light from shiny objects may be detected from any position, detecting the retro-reflected light will be successful only if the optical receiving means  54  is either totally or partially within the defined retro-reflected light zone. Another way of saying this is that the optical receiving means  54  and the illumination output source  30  must be “on-axis” (or “very near”) with each other in order for the optical receiving means  54  to receive the retro-reflected light. Otherwise, if the optical receiving means  54  is placed completely outside the retro-reflected light zone (so that it is “off-axis” from the illumination output source  30 ), it will no longer be able to detect the retro-reflected light, between rays  50  and  52 . However, it will still be able to detect both diffusely scattered light and reflected light from shiny objects. 
     Light emitted from source  30  illuminates an area, broad or narrow in dimension, defined by the rays  36  and  38 . Thus, the space in between rays  36  and  38  is illuminated by the source and the space outside rays  36  and  38  is not illuminated by the source. Output source  30  may be comprised of any type of light source, such as a light bulb (with or without a filter), an LED, optical fiber, or a laser. Furthermore, the light emitted from output source  30  may originate from some outside control optical and/or electronic system  34 , and such light may be transmitted via optical transfer means  32  to the output source  30  for emission. Furthermore, output source  30  may or may not include beam-shaping optics such as a holographic diffuser, an optical fiber, a lens, a line generator, a mirror, a diffraction element, etc. Furthermore, output source  30  may emit electromagnetic radiation at any wavelength or range of wavelengths, including ultraviolet (0.1-0.4 micron), visible (0.4-0.7 micron), and infrared (0.7-15 micron). 
     When a target imaging system  40  is inside the space that is illuminated by the source  30 , it will retro-reflect part of the source illumination. The term target as used herein refers to any optical detection device whose presence and/or location is to be determined by the user of the present invention. Such a device will generally include a housing  42  fitted with an objective lens  44  of either the refracting or reflecting type. It may include an eyepiece  46  to view the image formed by the objective lens. It may also include an imaging plane  48 , which may consist of a CCD array, micro-channel plate, photo-diode array, image intensifier tube, diffusing screen, or otherwise. In the case that an imaging plane  48  is not included, a human eye is used behind the eyepiece  46  for viewing. Furthermore in this case, the human retina is the location where the image is formed by the objective lens and therefore it is the human retina in this case that serves as the imaging plane  48 . 
     Light from the imaging plane  48  is retro-reflected back out through the objective lens  44 , and is nearly collimated in the direction from which it originally was incident on the objective lens (that is, it is nearly collimated in the direction of the light source  30 ). This retro-reflected light is confined between ray paths  50  and  52 . Therefore, in order for the present invention to work, an optical receiving means  54  of some type (such as a human eye, or a CCD camera, or an optical fiber, or a photodetector), with or without its own set of imaging optics, must be placed at least partially within the defined retro-reflected light zone of the on-axis illuminator  30 , so that said optical receiving means  54  can intercept some or all of the retro-reflected light between rays  50  and  52 . 
     FIG. 3 shows a schematic diagram of a preferred embodiment of the apparatus  70  of the invention. All parts of apparatus  70  of the invention are contained within or connected to a housing  72 , which in this case is made of aluminum, but may be made of any durable material such as plastic, wood, or metal. The miniature telescope  74  (preferably manufactured by Tasco, purchased through Edmund Scientific, part #Y1568) is mounted into the housing  72 . In front of the telescope  74  is a polarizing beamsplitter  76  (preferably by Spindler &amp; Hoyer, part #33 5561), which is glued or otherwise affixed to a mounting post  78 . A laser diode module  80  (preferably a red, 635 nm wavelength laser, such as one made by Thorlabs, part #CPFS63AP05ME) is mounted to the housing  72  with forward mounting post  82  and rear mounting post  84 . It is important to note that although a red, 635-nm wavelength laser diode  80  is preferably utilized as the on-axis illuminator in this particular embodiment, the invention is not limited to any particular color, wavelength, or style of light source (laser, LED, lamp, etc.). The laser diode module  80  is connected via electrical wires  86  and  88  to the power supply board  90  (preferably stock item from MondoTronics). A power source such as a 9-volt battery  92  (Energizer, part #522) is connected via electrical wires  94  and  96  to the power supply circuit or board  90 . An on/off switch  98  and on/off indicator LED  100  (included with MondoTronics power supply board  90 ) are also connected to the power supply board  90  and mounted into the housing  72 . The above specific examples of components are provided as illustrative examples of workable components within the present invention. It should be realized that these components can be varied and substituted for by a wide range of equivalents all within the spirit and scope of this invention. 
     Preferably, in this embodiment, red light  102  emanating from the laser diode module  80  is aimed at the beamsplitter  76 . The laser diode module  80  is aligned in its mounting posts  82  and  84  such that its polarization is aligned with the beamsplitter&#39;s  76  reflection polarization orientation. This way, the vast majority of red laser light  102  is reflected as beam  108  out of the housing, and only a very small portion is allowed to pass directly through as beam  112  the beamsplitter  76  to hit a diffusing beam block  114  (preferably a soft piece of Velcro®). Red light that is reflected  108  from the beamsplitter  76  first passes by a green filter  104  (without passing through it) and then passes through a polarizing filter  106  (which is oriented to allow the maximum amount of laser light  108  to pass through it) before exiting through an aperture  110  (which may in certain circumstances be covered by a transparent member, and may even include a filter) in the housing  72 . Light from the scene being observed  116  along with retro-reflected red laser illumination  118  enters the aperture  110  in the housing  72 . Both the scene light  116  and the retro-reflected red light  118  pass through the polarizing filter  106 . The retro-reflected light  118  then passes by the green filter  104  without passing through it. Some of the retro-reflected light  118  also passes directly through the beamsplitter  76 . Finally, the retro-reflected light  118  enters the telescope  74 . Most of the scene light  116  passes through the green filter  104  (although a small portion does pass by it without passing through it). The scene light  116  then also enters the telescope  74 . The entire scene, including scene light  116  which has passed through a green filter  104  and retro-reflected red laser illumination light  118 , is finally viewed through the telescope&#39;s eyepiece  120 . 
     FIG. 4 shows a front-on diagram of the partial green filter  104 . This is the view as seen looking into the aperture  110 . Note that in this view, the green filter  104  is partly obscured (denoted by dashed lines in the figure) by the housing  72  so that only a portion of the green filter  104  is visible through the aperture  110 . Note also that the filter is cut out so that it does not obscure the beamsplitter  76 , nor does it obscure any of the nearby surrounding area of the beamsplitter  76 . Note that the mounting post  78 , to which the beamsplitter  76  is attached, is also shown in the figure. The reason for the green filter  104  (which covers most of the input aperture  110  except for the portion in the vicinity of the beamsplitter  76 ) is to block most of the red light out of the scene light, so that the scene appears greenish in tint. This way the only time that the user will see red light is if red light passes by the green filter without passing through it (all other red light is blocked by the green filter). By virtue of the nature of the principle of retro-reflection described in FIG. 2 above, the majority of red light that passes by the green filter  104  without passing through it will be retro-reflected light. Thus, the entire scene will appear green in color unless an imaging system is in the field of view. In that case, the imaging system will appear as a bright red spot to the user. This partial green filter acts to greatly improve the contrast and therefore the effectiveness of the invention. Once again, it is important to note that the color of the green filter  104  is provided as an illustrative example of a workable component within the present invention. Specifically, the color of the green filter  104  is chosen such that it does not transmit light from the on-axis illuminator, which illuminator in this case consists of a red laser diode module  80 . It should be realized that the color and style of this filter can be varied and substituted for by a wide range of equivalents all within the spirit and scope of this invention. For example, a blue filter may be used instead of the green filter  104 . 
     The reason for the polarizing filter  106  is threefold. First, the polarizing filter  106  keeps foreign objects (fingers, paper clips, dust, etc.) out of the housing. Second, the polarizing filter  106  makes it difficult to view the device interior and thus observe the components that make up the system, giving the package a more finished-looking outward appearance. Finally, the polarizing filter  106  allows all the laser light, which is polarized, to pass directly through it while only allowing a fraction of the scene light to pass through. This helps to make the retro-reflected laser light stand out from the background. 
     With the embodiment of FIG. 3, shiny objects (such as glass, metal, etc.) also reflect red light. One drawback with this preferred embodiment is that there are occasional false alarms, as some shiny objects also appear red. This one drawback is addressed and improved upon in the following further embodiments. 
     Further embodiments of the apparatus of the present invention are set forth below. In these embodiments, for clarity, common elements and components described in the various embodiments of this invention will be designated by identical reference numerals. 
     As shown in FIG. 5, a second illumination output source  111 , called an “off-axis illuminator” (which may or may not be connected, via optical and/or electronic means  112 , to control electronics and/or optics  114 ), is present. The definition of an “off-axis illuminator”  111  is an illumination source that is “off-axis” (or “far away”) from the optical receiving means  54 . In practice, “off-axis” or “far away” means that there should be preferably about 4 cm of distance between the off-axis illuminator  111  and the optical receiving means  54  for every 3meters of distance between the optical receiving means  54  and the target imaging system  40 . This off-axis illuminator  111  has nearly the same direction of illumination as the first illumination output source  30 . This off-axis illuminator  111  may emit light of the same electromagnetic wavelength(s) as or different electromagnetic wavelength(s) than the on-axis illuminator. An important factor is that the off-axis illuminator  111  be located enough of a distance away from the optical receiving means  54  so that significant retro-reflection (shown in FIG. 5 between rays  120  and  122 ) of its illumination is not seen by the optical receiving means  54  (see FIG. 5, and compare with FIG.  2 ). Thus when the on-axis illuminator  30  is turned on, the optical receiving means  54  will see not only retro-reflected light (between rays  50  and  52 ) from a target imaging system  40  but it will also see reflected light from other shiny objects. However, when only the off-axis illuminator  111  is turned on, the optical receiving means  54  will not be able to see the retro-reflected light from the target imaging system  40  (between rays  120  and  122 ), but it will see reflected light from other shiny objects. 
     The method of operation for this embodiment involves switching the on-axis illuminator  30  on and off, while either keeping the off-axis illuminator  111  on constantly or switching the off-axis illuminator  111  on and off in such a way that at least one of the two illuminators ( 30  and  111 ) is emitting at any given time. FIG. 6 gives an example of what the on/off cycle for the two illuminators might be. The key here is to switch the on-axis illuminator on and off at some frequency (preferably between 1 Hz and 10 MHz), while ensuring that at least one illuminator is emitting at all times. In this manner the detector will see the reflections from shiny objects as being constantly illuminated, while the retro-reflections from a target imaging system will appear to blink at the on/off switching frequency used to control the on-axis illuminator. Using this method, it is possible to eliminate false alarms (since reflected light from shiny objects will not blink), and ensure that target imaging systems stand out from the background (because retro-reflected light from target imaging systems will blink at the given frequency at which the on-axis illuminator is switched on and off). If electronic light-detection means are not used, then both the on-axis illuminator  30  and the off-axis illuminator  111  must emit radiation at any wavelength or range of wavelengths in the visible regime (0.4-0.7 microns) and must be pulsed at a frequency slower than 60 Hz in order to be visible to the user. 
     Also, a photodiode, a CCD array, or other opto-electronic photosensor may be used in the optical receiving means  54  or in its associated control optics and/or electronics  58 . From the point of view of the optical receiving means  54 , the on-axis illuminator  30  will produce target camera retro-reflection plus shiny object reflection, while the off-axis illuminator  111  will produce only shiny object-reflection. Therefore subtraction of the second signal from the first will yield only target camera retro-reflection. This can be done by electronically subtracting the photoelectric signal (which is received by the optical receiving means  54 ) when output from the off-axis illuminator  111  is pulsed from the photoelectric signal (which is received by the optical receiving means  54 ) when output from the on-axis illuminator  30  is pulsed. Since electronic light-detection means are used, the illuminators ( 30  and  111 ) may operate at any wavelength or range of wavelengths, including ultraviolet (0.1-0.4 micron), visible (0.4-0.7 micron), and infrared (0.7-15 micron). 
     Processing electronics may be used to produce as output to the user any combination of a visual display (a small TV screen, an indicator LED or lamp, or a series of indicator LEDs or lamps), an audible output (a beep, buzz, click, or tone), or recorded data. 
     FIG. 7 shows a schematic diagram of another preferred embodiment of the invention in the form of apparatus  200 . All parts of apparatus  200  of the invention are contained within or connected to a housing  201 , which in this case is preferably made of aluminum, but may be made of any durable material such as plastic, wood, or metal. A telescope  202  in the form, for example, of a miniature Galilean Telescope is mounted firmly to the housing  201 . The Galilean Telescope  202  includes a positive lens  204 , preferably a 25 mm diameter 100 mm focal length plano-convex lens (Edmund Scientific part #H32482), a linear polarizing filter  205  (Optosigma part #069-1105), which filter is oriented to maximize transmission of retro-reflected laser light  226 , and a negative lens  206 , preferably a 12 mm diameter 48 mm focal length plano-concave lens (Edmund Scientific part #H45019). All parts  204 ,  205 , and  206  of the Galilean Telescope  202  are aligned with respect to one another inside a sturdy lens-mount tube  207 . Attached to the end of the Galilean Telescope  202  is any suitable rubber eye-cup  208 . Mounted in front of the other end of the Galilean Telescope  202  is a flat piece of clear glass  210 , preferably a 1-inch diameter, 3.3 mm thick, anti-reflection coated float glass window (Edmund Scientific part #H46098) to which a small prism  212 , preferably a 2 mm right-angle glass prism (Edmund Scientific part #H45524), has been affixed, preferably using a clear optical cement such as Norland Optical Adhesive  68  (Edmund Scientific part #H36427). Orientation of the prism  212  with respect to the glass window  210  and on-axis laser  220  is as shown in FIG.  7 . Also mounted inside the housing  201  is an electronics board  214 . Electronically connected via electrical wires to the electronics board  214  are the following components: a power source such as a battery  216 , preferably 9 volts, on/off switch  218 , on-axis laser  220 , and off-axis laser  228 . 
     A schematic circuit diagram for the electronics board  214  is shown in FIG.  8 . An example of an electronics board  214  capable of being used with the present invention comprises, for illustrative purposes and not for limitations on the invention, the following electronic components, wired together as shown in the schematic circuit diagram shown in FIG.  8 : MIC5205-5.0BM5 voltage regulator  300 , 470 pF capacitor  302 , 2.2 μF capacitor  304 , 2.7 MΩ resistor  306 , 432kΩ resistor  308 , 100 nF capacitor  310 , 10 nF capacitor  312 , LMC555 timer IC chip  314 , 2.21 kΩ resistor  316 , MMBT2222 transistor  318 , 1.0 kΩ resistor  320 , MMBT2222 transistor  322 , 2.21 kΩ resistor  324 , and MMBT2222 transistor  326 . 
     The above and following specific examples of components making up the apparatus  200  and electronics board  214  are provided as illustrative examples of workable components within the present invention. It should be realized that these components can be varied and substituted for by a wide range of equivalents all within the spirit and scope of this invention. 
     Also shown in FIG. 8 are the following examples of components used with this invention (which are electronically connected via electrical wires, as shown in the schematic diagram, to the electronics board  214 ): battery  216 , preferably 9 volts, on/off switch  218 , on-axis laser  220 , and off-axis laser  228 . The electronics board as shown will cause the on-axis laser  220  and the off-axis laser  228  to flicker alternately, with the on/off pattern of each laser as shown in FIG.  9 . Thus, both the on-axis laser  220  and the off-axis laser  228  flicker at preferably 4 cycles/second. Also, when the on-axis laser  220  is on, the off-axis laser  228  is off and vice versa. Furthermore, the on-axis laser  220  is run at preferably a 10% duty cycle, while the off-axis laser  228  is run at preferably a 90% duty cycle. It is important to note that the above specific examples of flicker frequency and duty cycles for the on-axis laser  220  and the off-axis laser  228  are provided as illustrative examples of workable frequencies and duty cycles within the present invention. It should be realized that these frequencies and duty cycles can be varied over a wide range within the spirit and scope of this invention. 
     Referring again to FIG. 7, the on-axis laser  220  is preferably a 635 nm red laser diode module (Thorlabs part #CPS63AP05ME) with a positive lens  221 , preferably a small, plastic asphere lens (Thorlabs part #CAX183), mounted on the front to properly focus the on-axis laser beam  222  onto the small prism  212  before allowing the beam  224  to diverge as it exits the housing  201  through the main aperture  225 . It is important to note that although a red, 635-nm wavelength laser diode is described in this particular embodiment, the invention is not limited to any particular color, wavelength, or style of light source (laser, LED, lamp). The off-axis laser  228  is preferably identical to the on-axis laser  220 . Thus the off-axis laser  228  is preferably a 635 nm red laser diode module (Thorlabs part #CPS63AP05ME) with a positive lens  229 , preferably a small, plastic asphere lens (Thorlabs part #CAX183), mounted on the front to focus the off-axis laser beam  230  to allow an output beam  232  that is nearly identical to the output beam  224  from the on-axis laser  220 . Laser beam light  232  from the off-axis laser  228  exits the main housing  201  through the secondary aperture  234 . For best effect, the off-axis laser  228  is mounted so that its beam  232  emerges from the secondary aperture  234  almost parallel with the exiting beam  224  of the on-axis laser  220  such that at a preselected distance from the exiting beams the beams  224  and  232  overlap in order to ensure that an area is identically illuminated by both beams. More specifically and for purposes of illustration but not as a limitation on this invention, the two exiting beams  224  and  232  exit the housing  201  at points preferably, but not limited to, approximately 4 cm apart. Both the on-axis laser  220  and the off-axis laser  228  are oriented and made, with the addition of positive lenses  221  and  229 , to diverge so as to fill the vertical field of view of the Galilean Telescope  202 . Furthermore, the two lasers  220  and  228  are co-aligned so that their two laser beams overlap at a distance of about  10  feet from the apertures  225  and  234 . FIG. 10 shows in exaggerated fashion a representation of the co-alignment of the two lasers  220  and  228 , which co-alignment results in the overlap of the two laser beams at a distance of about 10 feet from the device. 
     Referring again to FIG. 7, retro-reflected laser light  226 , along with light from the scene being viewed, enters the Galilean Telescope  202  through the main aperture  225  in the housing, and is detected in the same manner as through telescope  74  with respect to FIG.  3 . It is again to be noted that the specific components set forth above are provided as working examples but may also be substituted for by equivalent components which fall within the purview of the present invention. 
     In a still further embodiment of this invention, alternating very short pulses from each of the two illuminators of the type described with respect to the embodiments of FIGS.  5  and/or  7  are used (instead of requiring that at least one of the two illuminators be on at any given time). FIG. 11 provides an example of a typical on/off cycle for the two illuminators. The object is to use light pulses that are so short as to be undetectable by either the human eye or by an electronic video camera (between 0.01 and 100 microseconds long). This way, use of the invention will be undetectable by the target imaging system  40 . Referring to FIG. 5, the optical receiving means  54  and/or the control optics and/or electronics  58  in this case would include either a relatively fast-response photodetector or a CCD system that is set up to integrate the signal over many pulses (called a time-integrating CCD system). This results because a typical CCD array or human eye would not be able to detect the short pulses of the retro-reflected signal. To. prevent the time-integrating CCD system from saturating with normal room lights, a filter could be used that passes a very narrow band of wavelengths around the illumination wavelength. 
     The detection system would be able to distinguish between shiny object reflection and target camera retro-reflection in the same manner as described above. Since electronic light-detection means are used, the illuminator  30  may operate at any wavelength or range of wavelengths, including ultraviolet (0.1-0.4 micron), visible (0.4-0.7 micron), and infrared (0.7-15 micron). The output from the device would be similar to that described above. 
     A still further embodiment of this invention is also similar to the embodiment set forth in FIG.  5  and therefore FIG. 5 is also referred to with respect to the embodiment of the invention where the difference is the color or electromagnetic wavelength(s) of the off-axis illumination source  111 . In this embodiment of the invention, the color or wavelength(s) of light from the two illumination sources  30  and  111  is different: for example, the off-axis source  111  may be green and the on-axis source  30  may be red. Both illumination sources may be left on continuously, without switching on and off. However, nothing precludes this embodiment from functioning if the illumination sources are switched on and off. With this modified arrangement of the embodiment shown in FIG. 5, the optical receiving means  54  will see reflected light from shiny objects from both the on-axis source  30  and the off-axis source  111 , simultaneously. This red and green reflected light is additive and will appear to the optical receiving means  54  and/or its associated control optics and/or electronics  58  as yellow light. However, retro-reflected light from a target camera will appear to the optical receiving means  54  and or its associated control optics and/or electronics  58  as red light. This is because green retro-reflected light (which originated from the off-axis source  111 ) will follow the path between rays  120  and  122 , and will not reach the optical receiving means  54 . Meanwhile, red retro-reflected light (which originated from the on-axis source  30 ) will follow the path between rays  50  and  52 , and will reach the optical receiving means  54 . Thus, shiny reflective objects will appear yellow and retro-reflecting target imaging systems  40  will appear red to the optical receiving means  54  and/or its associated control optics and/or electronics  58 . This apparent contrast can be enhanced with the use of a yellow filter (not shown) in front of the optical receiving means  54  and/or before the associated control optics  58 . This way, the background scene will appear yellow, shiny reflective objects will appear bright yellow, and retro-reflecting target imaging systems  40  will appear very bright red. 
     If electronic light-detection means are not used, the illuminator  30  must operate at any wavelength or range of wavelengths in the visible regime (0.4-0.7 microns) in order to be visible to the user. If electronic light-detection means are used, then the illuminator  30  may operate at any wavelength or range of wavelengths, including ultraviolet (0.1-0.4 micron), visible (0.4-0.7 micron), and infrared (0.7-15 micron). 
     FIG. 12 shows a schematic diagram of an even further embodiment of this invention. FIG. 12 shows the addition of (second) optical receiving means  130  (called the off-axis optical receiving means), which may or may not be connected via optical and/or electronic means  132  to control electronics and/or optics  134 , to the setup shown in FIG.  2 . This way, the off-axis optical receiving means  130  is able to see reflections from shiny objects, but is not able to see target camera  40  retro-reflection, which is confined to the area between ray  50  and ray  52 . However, the on-axis optical receiving means  54  is able to see both shiny object reflections and target camera  40  retro-reflection. By using a binocular imaging system for the two optical receiving means  54  and  130 , the user would see the same background image in both eyes, the same shiny object reflection in both eyes, but would see target camera  40  retro-reflection in only one eye. For example, if the left tube of a pair of binoculars were used as the on-axis optical receiving means  54 , and the right tube of the same pair of binoculars were used as the off-axis optical receiving means  130 , then the user would see the background image and shiny object reflections in both his left and right eyes. But the user would see target camera retro-reflections in only his left eye. This improvement would help the user distinguish between target camera retro-reflection and shiny object reflection. If electronic light-detection means are not used, the illuminator  30  must operate at any wavelength or range of wavelengths in the visible regime (0.4-0.7 microns) in order to be visible to the user. 
     Furthermore, by using electronic light-detection means (such as a photodiode, a CCD array, or some other opto-electronic photosensor) in optical receiving means  54  and  130  and/or their associated control optics and/or electronics  58  and  134 , it will again be possible to subtract the off-axis optical receiving means&#39;s  130  electronic signal from the on-axis optical receiving means&#39;s  54  electronic signal, to result in only the signal received from retro-reflected target camera light, as described previously. Since electronic light-detection means are used, the illuminator  30  may operate at any wavelength or range of wavelengths, including ultraviolet (0.1-0.4 micron), visible (0.4-0.7 micron), and infrared (0.7-15 micron). Once again as before, the output may be visual, audible, or recorded data, as described previously. 
     An even further embodiment utilizes short pulse illumination in conjunction with the embodiment of FIG.  12 . The short pulses (see FIG. 11) are used to evade detection by the target camera. Also, the optical receiving means  54  and  130  and/or their associated control optics and/or electronics  58  and  134  must include either a relatively fast-response photodetector or a long-time-integrating CCD, since a typical CCD array or human eye would not be able to detect the short pulses of the retro-reflected signal. Since electronic light-detection means are used, the illuminator  30  may operate at any wavelength or range of wavelengths, including ultraviolet (0.1-0.4 micron), visible (0.4-0.7 micron), and infrared (0.7-15 micron). The photodetectors would be able to distinguish between shiny object reflection and target camera retro-reflection by subtracting the signal seen by the off-axis optical receiving means  130  from that seen by the on-axis optical receiving means  54 . The output from the device would be visual, audible, or recorded data, as described previously. 
     If electronic light-detection means are not used, the illuminator  30  must operate at any wavelength or range of wavelengths in the visible regime (0.4-0.7 microns) in order to be visible to the user. If electronic light-detection means are used, then the illuminator  30  may operate at any wavelength or range of wavelengths, including ultraviolet (0.1-0.4 micron), visible (0.4-0.7 micron), and infrared (0.7-15 micron). 
     Another embodiment of the present invention utilizes optical fibers as part of either the illumination source or the detection system, or both. An example of such system is shown in FIG.  13 . In this example, the illumination system  30  from FIG. 12 is replaced by a light source  412  (such as a laser diode, LED, incandescent lamp, etc.) connected to an optical fiber  410 . The optical fiber illuminates an area bounded by rays  36  and  38 , as before in FIG.  12 . The return illumination is detected by a pair of fibers. An on-axis fiber  414  couples light to a photosensor  416  and thus acts in a manner similar to the on-axis optical receiving means  54  described above. Finally, an off-axis fiber  418  couples light to a separate photosensor  420  and thus acts in a manner similar to the off-axis optical receiving means  130  described above and shown in FIG.  12 . Operation of this device would otherwise be exactly as described with respect to the embodiment shown in FIG. 12, with the illumination output source  30  replaced by laser  412  and fiber  410 , the on-axis optical receiving means  54  replaced by fiber  414  and photosensor  416 , and the off-axis optical receiving means  130  replaced by fiber  418  and photosensor  420 . 
     A still further embodiment uses some form of automated or semi-automated scanning action in conjunction with any of the above embodiments that involves use of detection by an electronic means. The concept presented in this embodiment is to have the device automatically scan a room and give feedback to the user in the form of a visual display, and audible report, or recorded data as to the location and/or presence of hidden cameras. One possible way to create the scanning action would involve the use of a motorized, computer-controlled pan/tilt device, as found in typical camera equipment. FIG. 14 shows an example of this embodiment. In this embodiment, a housing  350  is firmly attached to a motorized pan/tilt device  352 . Any of the previously-described embodiments (such as those shown in FIG. 2, FIG. 3, FIG. 5, FIG. 7, FIG. 12, or FIG. 13) may be contained inside the housing  350 . An electrical cable  358  connects the pan/tilt device  352  to a computer  354 . An electrical and/or optical cable  356  connects the housing  350  to computer  354 . The computer  354  and pan/tilt device  352  act together, as a standard computer-controlled pan-and-tilt system, to effect panning and tilting motion of the housing  350 . Connection of the housing  350  to the computer  354 , via an electrical and/or optical cable  356 , allows the computer access to data obtained by the embodiment of the present invention contained within the housing  350 . 
     Although the invention has been described with respect to various embodiments, it should be realized this invention is also capable of a wide variety of further and other embodiments within the spirit and scope of the appended claims. For example, other embodiments of this invention include the following improvements: One allows the user the ability to change the angle of output from the illumination system. This improvement can be used in conjunction with any of the previous embodiments. This concept is based upon moving an aperture, a mirror, a lens, or any combination or number of these items, in order to change the angle of illumination, and therefore the area of illumination. For example, a zoom lens may be used in front of the illumination system. This embodiment will allow the user to focus the illumination beam on a smaller area without having to walk up closer to the target camera. One reason this may be important is to prevent the target camera operator from knowing that the present invention has located the target camera. 
     Another embodiment involves the detection system being equipped with the ability to change its field-of-view. This embodiment can be used in conjunction with any of the previous embodiments as well. The idea behind this concept is that by moving an aperture, a mirror, a lens, or any combination or number of these items, the angle of detection, and therefore the area over which target cameras will be detected, can be changed. For example, a zoom lens may be used in front of (or incorporated into) the telescope shown in, for example, FIG.  3 . This improvement will allow the user to close in on a smaller area without having to walk up closer to the target camera. One reason this may be important is to prevent the target camera operator from knowing that the present invention has located the target camera. 
     A still further embodiment permits the system of this invention to work specifically at very long ranges (between 25 and 500 meters). Important aspects about a long-range system are that the angle between rays  36  and  38  of FIG. 2, for example, will be very small, and the angle between rays  116  and  118  of FIG. 3, for example, will also be very small. Also, the detection system will utilize a telephoto lens system in order to image scenes at long distances. 
     Even further embodiments include (1) the use of an illuminator and a filter in a single package that is designed to mount to a pre-existing camera or telescope or camcorder, etc. Thus the detector system is supplied by the user (in the form of a camera, camcorder, telescope, binoculars, etc.); and (2) hiding the above-described components inside a disguised package. For example, the invention can be packaged to look like a camera, or a camcorder, or a briefcase, or a pair of eyeglasses or sunglasses, or a hat. 
     Various further embodiments of the present invention are shown in FIGS. 15-26. These embodiments represent possible variations of the illuminator  30  and optical receiving means  54  and their associated control optics/electronics  34  and  58  used with the present invention and as shown, for example, in FIG. 2 of the drawings.