Visual Acuity Versus Field-of-View and Light Level for Night Vision Goggles (NVG).
Visual Acuity Versus Field-of-View and Light Level for Night Vision Goggles (NVG).

Author: Harry L. Task

Publisher:

Published: 1994

Total Pages: 21

ISBN-13:

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Parameters typically used to characterize night vision goggles (NVG) are visual acuity (resolution) and field-of-view (FOV). An increase in FOV is accomplished by providing higher magnification of the image intensifier tube. However, increased magnification means that the pixels will subtend a larger angle, thus leading to lower NVG visual acuity. An inverse relationship between visual acuity and field-of-view is expected based upon this optical/geometrical relationship. This relationship should be examined as production of NVG resolution quality increases. A trade-off study examining FOV and resolution was conducted with three observers having 20/20 corrected Snellen acuity. The NVGs had fields-of-view of 40, 47, and 52 degrees, respectively. Five levels of ambient scene illumination (corresponding to output luminance levels of 0.01, 0. 03, 0.08, 0.26, and 1.4 ft-L) were provided by a 2856K light source. The targets used in the study were 95+% contrast square wave targets ranging in size from 45 cycles/degree to 5 cycles per degree. A walk-back method of adjustment was employed. The results indicate that the geometric relationship between field-of-view and visual acuity is valid. Night vision devices, Visual acuity, Night vision goggles.

Night Vision Goggle Field-Expedient Visual Acuity Adjustment Procedures: Initial Experiment
Night Vision Goggle Field-Expedient Visual Acuity Adjustment Procedures: Initial Experiment

Author:

Publisher:

Published: 1996

Total Pages: 46

ISBN-13:

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The third-generation image intensification technology in night vision goggles (NVGs) used by ground forces provides at best 20/40 or 20/45 visual acuity. These acuity levels cannot be achieved unless soldiers adjust their NVGs properly. Documentation available to soldiers does not address optimum adjustment techniques developed by the aviation community nor does it address what can be used in the field to achieve a good setting. We examined the effectiveness and utility of 15 different objects commonly available to soldiers to determine which provided the best visual acuity readings with the AN/PVS-713 NVGs. After training and practice acuity improved by 25% over the baseline assessment. No large differences in readings occurred among the objects. However, a more definitive picture emerged when the average readings were combined with measures of variability and soldier preferences. The initial recommendation is to use one of the following objects for NVG adjustment: trec trunk, vehicle, vehicle trail, stars, blue chem light, or an infrared chem light. Not recommended are bright and/or red light sources, white paper, and trees silhouetted against the night sky. Problems in assessing acuity with NVGs are also discussed.

Measuring Observers' Visual Acuity Through Night Vision Goggles
Measuring Observers' Visual Acuity Through Night Vision Goggles

Author:

Publisher:

Published: 1998

Total Pages: 10

ISBN-13:

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Use of night vision goggles (NVGs) for military applications has grown steadily over the past 30 years. Each successive NVG model represents some kind of improvement in terms of size, weight, ruggedness, gain, noise, spectral sensitivity, field-of-view or resolution. The primary focus of this paper is the determination of NVG resolution. Many methods have been devised to measure the resolving power of NVGs and each method has with it an associated variance or accuracy of measurement. This variance is most likely caused by several sources including observer visual capability (since most methods involve visual observations and judgement to assess NVG resolution). The main purpose of this paper is to present the different methods that have been used to assess NVG resolution and to determine to what extent observer visual capability limits the accuracy of NVG resolution measurement. This study uses a methodology that measures an observer's psychometric function when viewing through NVGs (percent correct detection as a function of spatial separation) to determine their visual acuity using probit analysis.

Image Contrast and Visual Acuity Through Night Vision Goggles
Image Contrast and Visual Acuity Through Night Vision Goggles

Author: Jeff C. Rabin

Publisher:

Published: 1996

Total Pages: 8

ISBN-13:

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The purpose of this study was to investigate effects of display contrast and luminance on visual resolution through NVGs. Computer-generated letter charts were used to measure visual acuity across the range of luminances and contrasts one can encounter when viewing an NVG display. The results indicate that display luminance cannot, in itself, account for the level of acuity achieved through NVGs. Understanding the contrast and luminance transfer of NVGs is important for predicting human visual performance, and for developing improved night vision devices.

Evaluation of Night Vision Goggle: Visual Acuity Degradation While Wearing the FV-9 Laser Eye Protection Spectacle
Evaluation of Night Vision Goggle: Visual Acuity Degradation While Wearing the FV-9 Laser Eye Protection Spectacle

Author: Peter Demitry

Publisher:

Published: 1998

Total Pages: 22

ISBN-13:

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Of all man's senses, vision is recognized as the most critical for aviators to safely fly their aircraft (Tredichi, 1985). Since the introduction of night vision goggles (NVGs), night operations continue to become more demanding as aircrews continue to expand the night operational envelope. As mission variety expands, hazards likewise multiply allowing decreased margins for distraction, error or disorientation without deadly catastrophic consequences. NVGs provide an intensified image of night scenes illuminated by ambient energy in the red and near-infrared portion of the electromagnetic spectrum, which is abundant in the night sky. The intensified imagery is roughly 2,000 to 7,000 times brighter than the original scene, depending upon the type of intensifier tube used, and provides the user with a field of view ranging from 30 - 45 degrees (Kotulak & Rash, 1992). The explosion of NVG users attests to the fact that this technology greatly enhances the ability to conduct night operations. Goggles are used extensively in both rotary and fixed- wing aircraft. Law enforcement, immigration service and military aircrews increasingly rely on night vision devices when darkness restricts normal vision. NVG & work best when the ambient illumination is relatively intense (e.g., full moon) and the contrast of the scene is high. However, scene rendering is significantly degraded when ambient illumination decreases and/or scene contrast decreases (Kotulak & Rash, 1992).

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

Author: Joseph T. Riegler

Publisher:

Published: 1991

Total Pages: 30

ISBN-13:

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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.