Showing papers on "Night vision published in 1991"

Night vision backlighting system for liquid crystal displays

Abstract: This invention presents a way to provide night vision viewing compatibility of backlit electrooptic modulated light valve or LCD displays designed for daylight viewing. Liquid crystal displays (LCD) designed with backlighting systems which provide a high brightness, good contrast display under daylight conditions are inappropriate for use in dark, night time conditions where viewing of the display is desired utilizing electronic night vision equipment. This invention describes improvements to standard backlighting displays which through the utilization of arrays of low-level intensity light sources such as secondary fluorescent light sources, miniature incandescent lamps or light emitting diodes, the general means used in daylight vision can be turned off and the secondary low-level lighting sources achieve a minimum intensity acceptable for night vision electronic viewing.

Age-related eye disease, visual impairment, and driving in the elderly.

Abstract: As people age, a number of visual functions such as acuity, visual field, and night vision deteriorate. This decline in vision is associated in part with an increase in vehicular accidents per mile driven by the elderly. Four age-related ocular conditions--cataract, macular degeneration, open-angle glaucoma, and diabetic retinopathy--are primarily responsible for the decline in visual acuity and visual field in the elderly. Few epidemiologic data are available about these diseases, and at present they cannot be prevented. There is need for more information about visual decline and how it affects driving performance and for development of pragmatic approaches for detecting and assessing the elderly driver with functional visual deficits.

Modular day/night weapon aiming system

Abstract: The improved day/night weapon sight comprises a red dot aiming portion having a light emitting diode, a combining mirror, and an apparatus for mounting the LED and the mirror on a weapon to produce a virtual image of the LED at an infinite distance in alignment with the bore sight of the weapon, and a removable night vision portion having an objective lens, an eyepiece, and an image intensification tube for intensifying a received image intermediate the objective lens and the eyepiece, wherein the virtual image is visible to the operator at night through the eyepiece, and the night vision portion is removed for use of the red dot aiming portion during the day.

Day-and-night optical observation device

Abstract: A binocular-type optical device for night as well as day vision. A night vision optical device is located in a central body. The night vision optical device includes an optical path which is folded through a pair of opposed holes in a central body containing the night vision device. Two lateral bodies are affixed to the central body, each lateral body having a hole facing the holes in the central body. One of the lateral bodies faces an oblong hole in the central body, and is rotatable with respect to the central body. Each of the lateral bodies includes a day vision optical system having an objective at one end and an eyepiece at another end. A mirror contained in each lateral body are adjustable to permit either the folded night vision optical path or the day vision optical path to be received by a pair of common eyepieces.

Human Factors of Night Vision Devices: Anecdotes from the Field Concerning Visual Illusions land other Effects

Abstract: : To investigate the breadth of visual illusions experienced by aviators flying with night vision devices (NVDs), an open-ended questionnaire was distributed to the military helicopter community in the fall of 1989. Of the 242 returned questionnaires, there were 221 night vision goggle (NVG) reports and 21 thermal imaging system (FLIR) reports. Most sensory events occurred at night, during low illumination, good weather, and over varied terrain. Contributing factors included inexperience, division of attention, and fatigue. Frequently reported illusions were misjudgments of drift, clearance, height above the terrain, and attitude. Also reported were illusions due to external lights, and distributed depth perception caused by differences in brightness between NVG tubes. Other respondents cited hardware problems and physiological effects. There were no obvious differences between the experiences of NVG users and FLIR users. Although incidence rates cannot be inferred from these data, the variety of expected aviator anecdotes in this report will be useful to all those concerned with human factors and safety of NVDs.

Transmission mode InGaAs photocathode for night vision system

Abstract: An improved photocathode for use in a night vision system, comprising a glass face plate, an AlInAs window layer having an anti-reflection and protective coating bonded to the face plate, an InGaAs active layer epitaxially grown to the window layer, and a chrome electrode bonded to the face plate, the window layer, and the active layer providing an electrical contact between the photocathode and the night vision system, whereby an optical image illuminated into the face plate results in a corresponding electron pattern emitted from the active layer.

Night vision system and mounting assembly

Abstract: A night vision system usable as either a helmet mounted or face mask mounted monocular, or as a pocketscope, comprising an optical portion having an objective lens, an eyepiece, and an image intensification apparatus for intensifying a received image intermediate the objective lens and the eyepiece, a control housing affixed to the optical portion and having internal circuitry for powering the optical portion, and an apparatus for selectively mounting the monocular in an operational position adjacent to a desired one of an operator's eye and being rapidly switchable between the eyes.

Optical device designed for the introduction of a collimated image into an observer's visual field and enbaling night vision

Abstract: The disclosure relates to optical devices enabling daytime vision and night vision of an external scene with, in both cases, the superimposed introduction, into an observer's visual field, of an image given by an image generator. The image given by the light intensifier of a night observation system is processed in the same way as the image given by the image generator, by an auxiliary image-combining optical system which mixes these two images before they reach the main image-combining optical system of the device through which, in night vision, the observer directly sees the external scene. The auxiliary image-combining optical system is designed so that, in night vision, at least the greatest part of the light coming from the image generator reaches the main image-combining optical system. Depending on the embodiment, this result is obtained either with a retractable semi-reflecting mirror or with a semi-reflecting surface selective in frequency.

The Effect of Signal-to-Noise Ratio on Visual Acuity Through Night Vision Goggles

Abstract: : Since 1971, night vision goggles (NVGs) have been used by the military to enable personnel to perform visual operations in a nighttime environment. The key component of these devices is the image intensifier tube. Currently, no studies were identified which relate the signal-to-noise ratio (SNR) of image intensifiers to human visual acuity. The purpose of the present research was to determine the effect of NVG intensifier tube SNR on visual acuity. Visual acuity, using PVS-7 third generation NVGs, was measured for twelve participants at quarter moon and starlight illumination levels for four intensifier tubes with different SNRs. The range of SNR examined was 11.37 to 17.92. Visual acuity was assessed using Landolt C charts with target contrasts of 20 to 95 percent. The distance at which the acuity targets were resolved was recorded for each of the four illumination and contrast conditions. The results showed that increases in image intensifier tube SNR, illumination level, and contrast affected visual acuity. Regression analyses were performed to obtain estimated equations relating SNR to visual acuity for each experimental condition. The results were used to develop predictive guideline tables to provide approximate percent degradation/ improvement in visual acuity based upon intensifier tube signal-to-noise ratio.... Visual acuity, Night vision goggles, Signal-to-noise ratio, Image intensifier tubes.

Multi-focus system for a low light level vision apparatus

Abstract: A night vision apparatus 10 includes a first focusing refracting lens 28 which focuses light rays 29 from distant scene 14 onto a light intensifier 30. The kinoform 40 or bifringent lens 78 are disposed in the light path to allow light rays 35 from near scene 18, 20, 22 and 24 to be focused onto light intensifier 30 to form a multi-focus night vision apparatus with increased depth of focus.

Night vision aid for automobile

Abstract: The night vision aid uses an optical illumination device (BO) providing an IR beam (LB) with a difined polarisation and given beam angle, the reflected component of the emitted light having an orthogonal polarisation and received via an optical reception device (EO), supplying image information for a visual display. Pref. the illumination device (BO) provides a fan shaped beam (LB) with a narrow width in the perpendicular plane, with privoting of the beam relative to the latter.

Night vision goggle with improved optical system

Abstract: There is provided an improved night vision goggle having a housing containing an objective lens assembly, an image intensifier tube, a collimator assembly, a splitter member, and a pair of afocal telescopes. The optical axis of the afocal telescopes are offset from the optical axis of the collimator and objective lens assemblies. A pair of achromatic doublet lens assemblies are mounted side-by-side on the exit side of the collimator and near the entrance pupils of the telescopes. The optical axes of the doublet lens assemblies are coaxial with the optical axes of the telescopes. The achromatic doublet lens assemblies thus collect light from a sub-diameter, decentered aperture of the collimator assembly, and correct axial chromatic aberration in the telescopes.

Night vision scope with improved voltage supply

Abstract: A night vision scope (10) which includes an improved voltage supply (24). A battery (50) generates a voltage which is proportionally increased by a voltage step-up circuit (52) to provide a voltage to an image intensifier (20) and an infrared light source (16) of the night vision scope (10). The voltage supply (24) includes circuitry (56) for limiting the voltage output of the voltage supply circuit (24) if a battery (50) is used which generates a voltage greater than that required by the elements of the night vision scope (10).

Advanced high voltage power supply for night vision image intensifer

Abstract: The improved power supply of the present invention adjusts the voltages applied to an image tube to provide automatic brightness control and automatically compensate for temperature changes. A first oscillator, transformer and multiplier supply DC high voltage to a microchannel plate (MCP) electron multiplier of an image tube. The oscillator is controlled via control circuitry to modify the voltage applied to the MCP to automatically compensate for temperature changes associated with an image tube and to provide an automatic brightness control mode of operation. A second oscillator, transformer and individual multipliers are used to supply appropriate DC voltages to the cathode and screen of an image tube; these voltages are also automatically adjusted for temperature changes associated with the image tube. The screen current is detected and is used by additional control circuitry as feedback for the first oscillator to provide the automatic brightness control mode of operation. The power supply may separately adjust the operational voltage supplied to the MCP and the screen current needed to activate the automatic brightness control mode of operation.

Vanadium- and copper-containing glasses for use as filters for light sources intended for use with night vision devices

Abstract: The invention relates to a glass consisting essentially of ______________________________________ P 2 O 5 43-59 SiO 2 0-9 Al 2 O 3 7-11 Li 2 O 0-15 Na 2 O 0-15 K 2 O 0-15 MgO 0-15 CaO 0-0.5 BaO 0-7 ZnO 0-7 CeO 2 0-0.5 CuO 7-21 V 2 O 5 0.07-0.7 Pr 6 O 11 0-1.5 Nd 2 O 3 0-1.5 Nb 2 O 5 0-3 B 2 O 3 0-3 Y 2 O 3 0-3 Cr 2 O 3 0-1______________________________________ having a photopic transmission of at least 10% at full rated voltage and a color space of NVIS Green A or B. The glass is useful in the production of optical filters for use with light sources in order to render said sources compatible with night vision imaging systems.

A Visual Study of Migrating Owls at Cape May Point, New Jersey

Abstract: We studied the autumn migration of owls at Cape May Point, New Jersey, on 25 nights (178.5 hr) between 12 October and 11 November 1982 using visual and auditory techniques. We detected and observed migrating owls using an AN/PVS-3A night vision scope and 10X binoculars aided by moonlight, sky glow from a town, and the beam from a lighthouse. Barn (Tyto alba, 72.9%), Saw-whet (Aegolius acadicus, 8.6%) and Long-eared (Asio otus, 8.1%) Owls accounted for a majority of the 210 individuals counted. A comparison of the numbers of owls counted with those banded at Cape May Point during the same time period revealed a larger number and percentage of Barn Owls counted than banded, and a larger number and percentage of Saw-whet Owls banded than counted. Approximately one third of all owls were counted during the first two hours following sunset and disproportionately more owls were counted with light ( 10 m, which may account for their lower representation in the banding sample. Our observations show that visual and auditory techniques may be usefully employed in studying the nocturnal migration of owls, but also suggest that observational/ count studies of migrating owls may be subject to biases similar to those affecting diurnal count studies of migrating hawks.

Corneal lens goggles and visual space perception.

Abstract: Night vision goggles are head-mounted, unity-power systems designed to allow the human operator to see and operate at night. Field experience and experimental studies have revealed many drawbacks in conventional designs that impair performance. One major drawback is the poor space perception provided by the goggles. The Hadani et al. [ J. Opt. Soc. Am.70, 60– 65 ( 1980)] model for space perception attributes this drawback to the fact that the conventional designs shift the observer's effective center of perspective ∼15 cm ahead and also predicts the resulting impairments. An innovative redesign is presented in this paper—the corneal lens goggles (CLG)—which brings the effective center of perspective of the goggles to coincide with the center of perspective of the eyes, thus annulling the optical length of the device. Qualitative and quantitative laboratory studies have compared the performance of the CLG and conventional goggles (type AN/PVS-5). These studies have revealed better visual and visual-motor performance with the CLG. The implications to optical design of the Hadani et al. theory and the CLG concept are discussed.

Human Factors Issues in the Use of Night Vision Devices

Abstract: An account is given of the critical human factors that arise in field data on the differences between night vision displays and unaided day vision. Attention is given to the findings of empirical studies of performance on rotorcraft-flight-relevant perceptual tasks in which depth and distance perception are critical factors. Suggestions are made for man-machine-critical component design modifications in current night vision systems.

Remote fired RF getter for use in metal infrared detector dewar

Abstract: An infrared detector assembly (10) of the type used in munition and night vision systems having an RF activated getter (50). Such detector assemblies (10) include a tubular coldfinger (22) surrounded by a vacuum and which supports infrared detector array (26) and related components. In accordance with this invention, RF getter (50) is located remote from detector array (26) and engages an inner wall surface (56) of a metallic dewar housing (14). The RF getter (50) is activated via RF inductive heating directly through the metal dewar housing (14) such that sensitive IR detector components and hermetic braze joints are kept below their critical temperature. As a result, the present invention provides longer vacuum life and greater operational reliability of infrared detector assembly (10).

Human factors considerations in the development of an IVHS system - night vision enhancement

Abstract: This paper assesses Night Vision Enhancement systems as providing a potential means of enhancing visual detection at night.

[Progression of Bietti's crystalline dystrophy].

Abstract: Bietti's crystalline dystrophy is a rare form of tapetoretinal degeneration associated with numerous glittering deposits on the retina of the posterior pole and in the limbic part of the cornea. The case of a patient with Bietti's crystalline dystrophy followed-up for more than 5 years is described together with the changes seen during progression of the dystrophy. The patient was examined for the first time at the age of 27. At the last visit, marked impairment of night vision had developed, while there was no change in visual acuity. Ophthalmoscopic examination revealed that retinal crystals at the posterior pole were reduced in number, pigmented atrophy was more profound and that wide areas of choriocapillary atrophy had developed. There was a reduction in amplitude of the electroretinogram and the development of incomplete annular paracentral scotomas in the visual field. This case confirms that the symptoms of Bietti's dystrophy develop late and that progression of the dystrophy involves atrophy of the choriocapillary lamina and the choroid. At advanced stages, the disease may resemble a severe form of retinitis pigmentosa.

MTF optimization in lens design

Abstract: Designers are often asked to optimize the modulation transfer function (MiT) of a particular lens at specific fields and spatial frequencies. Use of a merit function related to mean square spot size or wave aberration to achieve these goals frequently requires considerable designer intervention. We describe an algorithm whereby diffraction MTF is optimized directly. The algorithm is efficient enough (i. e. on the order of five times the run time for classical techniques) to be used as a practical design tool. To illustrate use of the algorithm a previously designed night vision objective lens is reoptimized with the goal of increasing the MTF at a particular spatial frequency thus increasing the modulation margin allowed for tolerancing. Significant improvements in MTF and depth of focus are achieved with minimal designer effort and reasonable computation times. 1 .

Optical system for introducing a collimated image in the field of view of an observer and for night vision, and helmet comprising the same

Abstract: The invention relates to optical devices permitting day and night vision of the scenery with, in both cases, superimposed introduction of an image, which is supplied by an image generator (1), into the field of view of the observer. The image supplied by the light intensifier (6) of a night observation system (4-6) is processed in the same way as the image supplied by the image generator (1) by virtue of an auxiliary combining optical component (7-7') which mixes these two images before they arrive at the main combining optical component (3) of the device, through which main combining optical component, in day vision, the observer sees the exterior scenery directly. The auxiliary combining optical component is designed so that, in day vision, at least the greater portion of the light coming from the image generator reaches the main combining optical component. According to the embodiments, this is obtained either by a retractable semi-reflecting mirror or by a frequency-selective semi-reflecting surface (70). Application, in particular, to helmet display devices.

Visualization of gas tungsten arc weld pools

Abstract: : Surface flow visualization of Gas Tungsten Arc weld pools for HY-80 steel is presented using a pulsed laser light source and a conventional night vision image-intensifier tube equipped video camera. Visualization of the weld pool free surface is made possible by seeding a flow with alumina particles for both stationary and moving arc welds. These visualizations reveal several new features not incorporated in the existing models for stationary welds. A strong clockwise stirring is observed contrary to the axi symmetric computational models. Also, the pool surface shows a bulge near the center. Complex flow patterns are observed for moving arc welding. Interpretations of the observed flows based on the driving forces are provided.

Analysis of emissivity effects on target detection through smokes/obscurants

Abstract: The magnitude of target thermal contrast is used as a key parameter in determining whether observers using thermal-imaging systems can detect military targets. The effects of differences in target and background emissivities on thermal contrast estimates are evaluated, and the effects these differences have on the estimate of the transmittance attenuation thresholds required to obscure a target viewed with a thermal imager are examined. Target-background radiometric difference in the thermal infrared bands is first computed in terms of target-background emissivities and thermodynamic temperatures; the result is then used to compute a difference function for brightness temperature relative to thermodynamic temperature as a function of the target-background emissivity ratio. The effect of emissivity differences between targets and backgrounds on smoke/obscurant attenuation required to obscure a target viewed with a thermal imager is then examined using an expression derived from the Center for Night Vision and Electro-Optics Static Performance model. Results of the analysis show that smoke screen requirements for obscuring targets from thermal imager detection can change by factors of 10 as the ratio of target-to-background emissivity changes by less than 25%.

Eye scanning rules for drivers - how do they compare with actual observed eye scanning behavior?

Abstract: The U.S. driver education and training literature was reviewed to identify rules and/or recommendations with regard to driver eye scanning behavior and strategies, where a driver ought to fixate his eyes when driving, specifically when driving through a curve. In addition, driver eye scanning behavior was recorded and analyzed for 9 drivers driving through 240 feet radius right cruves (unlighted interstate entrance and exit ramps, 270 degree turns) at night with low beams. An instrumented car with a corneal reflection technique television eye scanning system was used. Each driver made a number of runs through the curves (average speed 26 mph) and the driver eye fixation sequences were analyzed for three to eight runs per driver, yielding a total of 51 analyzed runs. Results showed that the expected number of consecutive forward eye fixations (including forward ending eye fixations) is 1.89, while that of backward eye fixations (including backward ending eye fixations) is 1.26.