10 June 1994 Visual acuity versus field of view and light level for night vision goggles (NVGs)
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Abstract
Visual acuity (resolution) and field of view are two significant parameters used to characterize night vision goggles (NVGs). It is well established that these two parameters are coupled together in an inverse relationship: an increase in field of view results in a reduction in visual acuity and vice versa. An experiment was conducted to determine how visual acuity through NVGs changes as a function of NVG field of view and ambient scene illumination level. A total of three trained observers were used for this study who ranged in age from 33 to 42 years of age. The NVGs used in the study had fields of view of 40, 47, and 52 degrees, respectively. Five levels of ambient scene illumination (corresponding to NVG output luminance levels of 0.01, 0.03, 0.08, 0.26, and 1.9 fL) were provided by a 2856k light source which ranged from overcast starlight to quarter moon. The targets used in the study were approximately 95+% contrast square wave targets ranging in size from 45 cycles/degree to 5 cycles per degree. The method of adjustment was employed by having the trained observer start at a distance of 30 feet and determine the highest spatial frequency target which was clearly discernable. The subject was then directed to walk back slowly from the target until it was just out of focus, and then walk forward until the target was barely discernable. The distance from the target was recorded and used to calculate the angular spatial frequency (and equivalent Snellen acuity). The results indicate that the simple geometric model of the inverse relationship between resolution and field of view is adequate for characterizing this design trade-off for the quality of image intensifier tubes currently available.
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Mary M. Donohue-Perry, Mary M. Donohue-Perry, H. Lee Task, H. Lee Task, Sharon A. Dixon, Sharon A. Dixon, } "Visual acuity versus field of view and light level for night vision goggles (NVGs)", Proc. SPIE 2218, Helmet- and Head-Mounted Displays and Symbology Design Requirements, (10 June 1994); doi: 10.1117/12.177350; https://doi.org/10.1117/12.177350
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