Abstract:
Night vision devices utilize image intensifier tubes to see in low light conditions. A man-portable tester allows an operator to check for defects and determine the image resolution of the image intensifier tube quickly and easily without a power source or a darkened room.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional patent application Ser. No. 61/878,324 filed Sep. 16, 2013, the entire disclosure of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to test apparatus for night vision system with image intensifier tubes. 
     BACKGROUND 
     Soldier and law enforcement personnel use night vision devices, e.g. the AN/PVS-14, that include an image intensifier tube to allow them to see under very low light conditions. Before these devices are sent out on a mission they need to be tested to ensure they work properly. The most widely used image intensifier test set is the TS-4348/UV “Test Set, Electronic Systems” (a.k.a “Assessor”) and has been in production since approximately 1992 (see  FIG. 1 ). The TS-4348/UV is compact and lightweight. The functionality of the TS-4348/UV is controlled by MIL-PRF-49318A which states “The Assessor is a self-contained, battery operated, test device designed to provide a Go/No-Go check of the night vision systems . . . . ” The Go/No-Go check is accomplished by projecting a USAF 1951 bar target (a sample is shown in  FIG. 2 ) into a night vision system, at controlled light levels, in a manner that allows the resolution of the night vision system to be measured near the optical axis. The TS-4348/UV uniformly illuminates the field of view of the night vision system under test and illumination intensity is electronically controlled with precise opto-electronic feedback. The TS-4348/UV does not provide a means to identify defect (black spot and white spots) location or size, or for performing off-axis resolution tests. 
     The most common current method of identifying and measuring defects is with the use of a paper chart approximately 22.5″×30″ in size (see  FIG. 3 ) mounted on a wall. The test involves holding a night vision device 30″±1″ from the chart, viewing perpendicular to the chart, and centered on the concentric circles in a room whose light level can be adjusted from bright to dark. Black spots are identified with the room lights on, white spots are identified with the room completely dark, and other defects when the light level is low. Once defects are identified, the concentric rings are used to identify the zone in which the defect falls. The device is then repositioned to place the defect next to the black circles on the target which allow for defect size measurement. The number of defects and zones in which they fall are compared to a specification to determine the acceptability of the tube in a Go/No-Go style test. The wall chart does not provide a resolution test and requires a room with controllable lighting. 
     The Hoffman ANV-126A (see  FIG. 4 ) is a high end night vision tester with significantly more functionality than the TS-4348/UV or a wall chart. The ANV-126A performs resolution testing with a USAF 1951 bar target similar to the TS-4348/UV but with much greater electronic control over illumination levels and can perform defect zone mapping similar to a wall chart. A number of additional tests, such as measuring tube gain and tube current draw can also be performed which the TS-4348/UV, wall chart cannot perform. The drawbacks are in cost, complexity, and portability; an ANV-126A retails for approximately $40,000 while an Assessor is approximately $1000 and a wall chart less than $100. The weight of an ANV-126A exceeds 20 pounds while both the TS-4348/UV and wall charts are less than 1 pound each. The TS-4348/UV requires batteries to operate and the ANV-126A requires access to AC power. The TS-4348/UV and wall charts are commonly used in Army repair enclosures, such as the AN/ASM-146 or AN/ASM-147, while the ANV-126A is considered unsuitable for those environments. 
     The modern image intensifier tube dates back to the 1970&#39;s and was used in military devices such as the AN/PVS-4 night vision weapon sight and AN/PVS-5 night vision goggle. These early devices used what was referred to as 2 nd  generation image intensification tubes. Current state of the art night vision devices use 3 rd  generation image intensification tubes which function on the same principles as the 2 nd  generation tubes with some evolutionary improvements. Test equipment to evaluate and diagnose night vision devices with image intensification tubes has been developed over the years. Testers include the 1990&#39;s vintage TS-4348/UV low light resolution tester, wall charts, or the Hoffman Engineering ANV-126-001 night vision goggle tester, noted above. 
     Field test equipment is desirable to support logistics. Shipping damage, degradation during shipping, or failed vendor quality checks can lead to a new image intensifier tube being unsuitable prior to use. Good image intensification tubes are expensive and have a limited life span over which their performance will slowly degrade, and it is desirable to identify the point at which a tube has degraded to the point where replacement is merited. Finally, night vision systems are typically used in potentially hostile environments such as by the military, search and rescue, and police, which can result in a night vision system being damaged. When damage occurs, convenient methods and tools to diagnose the damage are needed in order to determine if repairs are needed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and advantages of the claimed subject matter will be apparent from the following detailed description of embodiments consistent therewith, which description should be considered with reference to the accompanying drawings, wherein: 
         FIG. 1  is a photo of a TS-4348/UV Test Set, Electronic System; 
         FIG. 2  is a sample 1951 United States Air Force resolution chart; 
         FIG. 3  is a “Black Spot Target” wall chart; 
         FIG. 4  is photo of a Hoffman ANV-126A; 
         FIG. 5  is a computer rendering of a night vision testing device consistent with a first embodiment of the present disclosure; 
         FIG. 6  is a section view of the night vision testing device of  FIG. 5 ; 
         FIG. 7A  is a isometric view of a night vision device spaced from the night vision testing device of  FIG. 5  and  FIG. 7B  is a isometric view of a night vision device inserted into an end of the night vision testing device of  FIG. 5 ; 
         FIG. 8  is a first embodiment of a target inside of the night vision testing device of  FIG. 5 ; 
         FIG. 9  is a computer rendering of a night vision testing device consistent with a second embodiment of the present disclosure; 
         FIG. 10A  is an isometric section view of the night vision testing device of  FIG. 9  in a first position,  FIG. 10B  is an isometric section view of the night vision testing device of  FIG. 9  in a second position, and  FIG. 10C  is an isometric section view of the night vision testing device of  FIG. 9  in a third position; and 
         FIG. 11  is an section view of the night vision testing device of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 5  is a computer rendering of a night vision testing device  100  consistent with a first embodiment of the present disclosure;  FIG. 6  is a section view of the night vision testing device  100 ;  FIG. 7A  is a isometric view of a night vision device  200 , shown as a monocular, spaced from the night vision testing device  100 ; and  FIG. 7B  is a isometric view of the night vision device  200  inserted into an end of the night vision testing device  100 . The testing device  100  allows identification of image intensifier tube  208  defects and determination of resolution operating in darkness, bright conditions, and high contrast lighting conditions. Identification involves determining the zone in which defect appears, the size of defect, and type of defect. The four most common defect types are dark spots, bright spots, scintillation, and chicken wire. 
     The testing device  100  may have a first portion  102  and a second portion  104  that pivots relative to the first portion  102 , for example, they may work like a ball-and-socket joint. The pivot allows the night vision device  200  to be rotated relative to a target  106 A in order to place target features in different areas of the night vision device field of view. In order to maintain a well focused image across the field without requiring mechanical adjustment of the night vision device this pivot is preferably placed close to the center of curvature of the spherically shaped target. On the second portion  104  may be a cover  106  which may house the target  106 A (see  FIG. 8 ). Optics  110  may include a optics and/or neutral density filter inserted in an opening  108  of the testing device  100 . The optics and/or neutral density filter may be located close to the entrance aperture of the night vision device  100  and may act to reimage the target  106 A onto the image intensifier tube of the night vision device. The distance at which the target appears to be from the night vision system under test may be configurable through optics  110 . Two typical apparent target distances are 30″ to mimic the standard dark spot wall chart test and infinity which is the commonly used as a zero diopter setting for test targets. The stop size of optics  110  may be chosen to balance aberrations, diffraction, and light throughput. The neutral density filter may have an optical density of 0 to about 3. 
     The opening  108  may be sized to accept an objective focus ring  206  of the night vision device  200 . The size of the opening  108  may be such that when the focus ring  206  is inserted into the opening  108 , a user can hold the night vision device  200  in one hand and the first portion  102  of the testing device  100  with the other hand, and when the night vision device  200  is rotated, the focus ring  206  is rotated relative to the night vision device  200 . The user can turn “on” the night vision device  200 , look through the eyepiece  202  and rotate the night vision device  200  relative to the first portion  102  to bring the target  106 A into focus. In an alternative embodiment, an insert may be inserted in the opening to change the diameter of the opening to accommodate objective focus rings of differing sizes. In an alternative embodiment, the interface at opening  108  may be an interchangeable component to accommodate different night vision devices. In an alternative embodiment, the user can hold the second portion  104  of the testing device  100  rather than the first portion  102 . 
     The second portion  104  of the testing device  100  may have a curved portion  104 A that cooperates with the first portion  102 ; a middle portion  104 B; and a base portion  104 C that may hold the cover  106 . The cover  106  may have a curved internal surface having a radius R upon which the target  106 A is disposed. The target  106 A may have a center ring  122 A sized that when viewed through the night vision device  200  corresponds to “Zone 1” of an image intensifier tube. Zone 1 may be sized to appear as a 0.22 inch diameter ring on the entrance of the image intensifier tube in the night vision device  200 . The target  106 A may have a second ring  122 B sized that when viewed through the night vision device  200  corresponds to “Zone 2” of an image intensifier tube. Zone 2 may be sized to appear as a 0.58 inch diameter ring on the entrance of the image intensifier tube in the night vision device  200 . The target  106 A may have a third ring  122 C sized that when viewed through the night vision device  200  corresponds to “Zone 3” of an image intensifier tube. Zone 3 may be sized to appear as a 0.71″ inch diameter ring on the entrance of the image intensifier tube in the night vision device  200 . The diameters of the zone may be changed without departing from the invention to match the requirements of different image intensifier tube specifications (e.g. “MIL-PRF-A3256363D(CR)”). The target  106 A may also have a series of measurement features  124 , for example circles of different sizes. The series of circles, when imaged through night vision device  200 , may range from approximately 0.003″ in diameter to approximately 0.015″ in diameter on the entrance of the image intensifier tube. The circles may be solid/filled in or hollow/not filled in. The size of the zones and the sizes of the circles may correspond to typical acceptance criteria for an 18 mm image intensifier tube or a particular image intensifier tube product specification. Similar targets may be used to inspect/test other sized image intensifier tubes without departing from the invention. The zones may be used to locate a defect in an image intensifier tube and the circles may be used to measure the size of each defect. The image tube specification may limit the size and quantity of defects by zone. A defect may be a black spot, a bright spot, “chicken wire” or scintillations. 
     Black Spots are cosmetic blemishes in the image intensifier tube, image intensifier tube defects, or dirt or debris in the optical path of a night vision device  200 . Black spots that are in the image intensifier can be inherent in the manufacturing processes or the result of damage. Black spots may be found when a predetermined amount of ambient light L 1 , natural or artificial, for example from a light source LS, for example a light bulb, travels through the testing device  100  and strikes the target  106 A. Black spots are best viewed when most of the ambient light L 1  strikes the target  106 A creating a brightly lit condition. 
     Bright spots are defects in the image area produced by the night vision device  200 . This condition may be caused by a flaw in the film on the image intensifier tube microchannel plate. A bright spot is typically a small, non-uniform, bright area that may flicker or appear constant. Bright spots are often imperceptible in environments with sufficient illumination for typical night vision device  200  operation. Bright spots are best viewed when little or none of the ambient light L 1  strikes the target  106 A creating a darkness condition. 
     Scintillations are faint, random, sparkling effect that may be found throughout the image area. Scintillation, sometimes called “video noise” despite an image intensifier tube not being a video device, is a normal characteristic of image intensifier with a microchannel plate and is more pronounced under typical night vision device  200  low-light conditions. Scintillations are best observed when a small amount of light L 2 , simulating starlight or moonlight, strikes the target  106 A creating a high contrast condition. 
     Chicken wire is a hexagonal pattern of dark thin lines resembling chicken wire fencing visible in the field of view either throughout the image area or in parts of the image area. If these hexagonal patterns become overly pronounced, replacement of the image intensifier tube may be merited. Image intensifier tube specifications contain specifications for the acceptable number, size, and zone location of pronounced chicken wire artifacts. Chicken wire is best observed when a small amount of light L 2 , simulating starlight or moonlight, strikes the target  106 A. 
     As noted above, the second portion  104  of the testing device  100  may be made of a diffuse light transmissive plastic, for example polytetrafluoroethylene (PTFE) thermoplastic polymer, or other material. The amount of ambient light L 2  that strikes the target  106 A may be varied in a variety of ways including varying the amount of light generated from the light source LS, for example with a light dimmer, by moving the testing device  100  away from the light source LS, or placing a light damper LD between the light source LS and the testing device  100 . 
     An operator may turn the night vision device  200  “ON” and then insert the focus ring  206  in the opening  108  of the testing device  100  and rotate the night vision device  200  relative to the first portion  102  of the testing device  100  until the target  106 A is in focus. The operator may locate a first defect and then determine what zone it is in by manipulating the night vision device  200  and the first portion  102  of the testing device  100  relative to the second portion  104  of the testing device  100  such that the first ring  122 A, second ring  122 B, and the third ring  122 C are concentric with illuminated field of view of night vision device  200 . The operator may then manipulate the night vision device  200  and the first portion  102  of the testing device  100  relative to the second portion  104  of the testing device  100  and the target  106 A to align the first defect next to one of the series of measurement features  124 . The operator may then compare the defect to the measurement features  124  to determine the defect size. The operator may then similarly determine the size of a second or subsequent defect. 
     Resolution is the ability of an image intensifier to distinguish between objects close together and is measured as a spacial frequency, typically using units such as line pairs per millimeter (lp/mm). Resolution is typically determined from a 1951 U.S. Air Force Resolving Power Test Target. The target is a series of different-sized patterns composed of three horizontal and three vertical lines. A user observes which of the bar patterns is the smallest that can still be distinguished as separate bars (e.g. not merged into a solid block). That smallest bar pattern is considered the resolution limit of the night vision device and is identified by the numbers next to the bar patterns (e.g. row/column numbers or group/element numbers). Because the 1951 USAF bar target requires high precision manufacturing methods to produce and may be difficult to place on a spherical surface, the 1951 USAF targets may be applied to one or more flat glass inserts which may be mechanically secured to the spherical target surface. In an alternative embodiment, an alternative test target such as a radial star, chirp, NBS 1963A or ISA/ISO may be used rather than a 1951 target. 
     The target  106 A may also have a resolution pattern  130 . The operator may turn the night vision device  200  “ON” and determine the center resolution of the image tube by manipulating the night vision device  200  and the first portion  102  of the testing device  100  relative to the second portion  104  of the testing device  100  such that the first ring  122 A, second ring  122 B, and the third ring  122 C are concentric with illuminated field of view of night vision device  200  and then by looking through the night vision device  200  and using known resolution techniques determine the appropriate resolution. The center resolution may be determined at any light level, but typically provides the best results when the amount of light L 2  striking the target  106 A is low, simulating star light or moon light illumination levels. 
       FIG. 9  is a computer rendering of a night vision testing device  100 ′ consistent with a second embodiment of the present disclosure;  FIG. 10A  is an isometric end section view of the night vision testing device  100 ′ with a first vane  120  in a first position;  FIG. 10B  is an isometric end section view of the night vision testing device  100 ′ with the first vane  120  in a second position;  FIG. 10C  is an isometric end section view of the night vision testing device  100 ′ with the first vane  120  in a third position; and  FIG. 11  is an end section view of the night vision testing device  100 ′ sliced through a base portion. Testing device  100 ′ may differ from testing device  100  in that it has the ability to control the amount of light L 2  that strikes the target  106 A. A plurality of actuators, for example pushbuttons  130 A,  130 B, and  130 C, may control the opening size of a mechanical aperture. Image intensifier tubes have automatic gain adjustment; and adjusting the light level allows the image intensifier tube to be tested under very low gain, high contrast, and very high gain conditions; which correspond to a brightly lit scene, dimly lit scene (starlight or moonlight), and dark scene respectively. The lower portion  104 ′ may diffuse the incoming light causing a more uniform illumination of the target  106 A, and therefore uniform illumination of the image intensifier tube in the night vision device  200  which may improve the ability to identify defects and determine resolution. 
     Internal to the second portion  104 ′ may be a first opaque vane  120  and a second opaque vane  126 . The second vane  122  may be fixed to, but spaced from, the second portion  104 ′. The first vane  120  may be movable relative to the second portion  104 ′ and the second vane  126 . Actuation of the actuators  130 A,  130 B, and  130 C may move the first vane from a first vane position shown in  FIG. 10A  to second vane position shown in  FIG. 10B  to a third vane position shown in  FIG. 10C . In the first position, the first vane  120  blocks the least amount of the ambient light L 1  passing through the second portion  104 ′; In the second position, the first vane  120  blocks more of the ambient light L 1  passing through the second portion  104 ′; and in the third portion  104 , the first vane  120  blocks the most ambient light L 1  passing through the second portion  104 ′. The actuators  130 A,  130 B, and  130 C may have a wedge, diamond, or cone shaped protrusion extending inwardly that cooperate with openings in the first vane  120  causing the first vane  120  to rotate relative to the second portion  104 ′ and the second vane  126 . 
     An operator may insert the focus ring  206  of the night vision device  200  in the opening  108 ′ to begin the testing and then manipulate the actuator  130 A,  130 B, or  130 C to adjust the amount of ambient light striking the target  106 A. 
     While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present invention. 
     All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. 
     The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified, unless clearly indicated to the contrary.