NVG Basics Flashcards
Light sensitivity
Frequency sensitivity well into near
IR range.
Minus blue coating for NVG
compatible cockpit
Light Amplification
Passive light amplification of 2500 - 10000+ times
Visual acuity
NVG 20/25 - 20/40
Unaided Day 20/20
Unaided night 20/200
Astigmatism
Magnification
NVG do not correct for Astigmatism
Magnification is 1:1, no magnification
Field of View FOV
Optimal FOV 40 Degrees
Unaided FOV 200+ Degrees
40 Degree FOV only obtained with Optimal Sight Adjustment Point OSAP Reduced FOV and peripheral vision Increase misperceptions and illusions, Proper scanning helps compensate.
Focal Range
NVG focal range 28 cm (+/-3cm) / 11 in (+/-1.2in) to Infinity
Infinity focus for NVG is
> 33 meters / 110 ft
Depth perception
Depth perception and distance
estimation are reduced compared
to unaided daytime.
Quality of both is effected by degree
of contrast, ambient lighting, viewer
experience utilizing monocular cues.
Peripheral vision
NVG mount allows for improved unaided vision for greater cockpit instrument visibility.
Operational temperature range
Weight and CG
125.6 F to -25.6 F (52 C to -32 C)
590 grams (20.8oz)
Detachability
NCG has 10-15g force breakaway capability
Monochromatic
The NVGs are monochromatic, single color viewing. Green or amber depending on the image intensifier type
Field of Regard FOR
The total area that the field of view can be scanned in the FOR. Head movements included.
Batteries
AA Alkaline - 10-22 hours of battery life
Monocular Components
Objective Lens Image Intensifier Tube Photocathode Micro Channel Plate Phosphor Screen Fiber Optic Inverter Power Supply Function Eyepiece Lens
Objective Lens
Optical element that gathers light, can be focused for the distance of the object.
Contains a minus blue coating which filters out light from the aircraft instruments.
Image Intensifier Tube
Electro-optical device that detects and amplifies light to produce and visual image.
Photocathode
Converts incoming light energy (photons) into electrical energy (electrons)
Micro Channel Plate
This wafer containing millions of hallow fiber optic channels. Increases the number and velocity of the electrons.
For every one electron that enters, thousands exit.
Phosphur Screen
A thin layer of phosphor that lights up as electricity hits it. Converts electrical energy back to photons.
Fiber Optic Inverter
A bundle of thin light transmitting fibers twisted 180 degrees to re-invert the picture upright for viewing.
Power Supply Function
Converts the 3.0 volts to the proper voltage required by the photocathode, micro channel plate, and phosphor screen.
ABC and BSP
Auto Brightness Control ABC
Auto Brightness Control (ABC) adjusts power to the Micro Channel Plate down under high light conditions and up under low light conditions to keep brightness within limits.
Bright Source Protection BSP
Bright Source Protection (BSP) adjusts voltage to the photocathode down when exposed to bright light sources..
Operational Defects
Relate to the reliability of the image intensifier and are an indication of instability. (4) of them: Shading, Edge Glow, Emission Points, Flashing/Flickering/Intermittent Operation
Shading
Each monocular should represent a full circle. Shading is when it doesn’t. Indicates a dying photocathode, begins at the edge and migrates inwards.
Edge Glow
Bright areas, sometimes sparkling, in the outer portions. Caused by an emission point outside the field of view, or a defective phosphor screen. To check, block out al light and bright spots that remain are edge glow.
Emission Points
Steady of fluctuating pinpoint of bright light in the image area.
Flashing/Flickering/Intermittent Operation
Commonly seen when adjusting the eye-span knob. If there is more than one flicker, check for loose wires, loose battery cap, or weak batteries.
Cosmetic Blemishes
Manufacturing imperfections that do not affect the image intensifiers reliability, not normally a cause for rejecting the NVG. Bright Spots, Black Spots, Chicken Wire, Image Distortion, Veiling Glare, Fixed Pattern Noise, Image Disparity, Output Brightness Variation
Bright Spots
Make sure its not from a bright light source. Caused by flaw in the film on the Micro Channel Plate. May flicker and not remain constant.
Black Spots
Cosmetic blemishes in the image intensifier, or dirt or debris between the lenses.
Chicken Wire
Irregular pattern of dark lines throughout the image area. Hexagonal or square shaped lines. Caused by fibers that do not transmit light at the boundaries or fiber bundles in the output optic of the image intensifier.
Image Distortion
Evidenced by vertical objects bending or waving when your head is moved horizontally or vertically. Should be screened for distortion at first use.
Veiling Glare
Light outside the NVG FOV hits the lens and scatters rather than passing through. Only under certain circumstances. Can be caused by scratched, pitted, or chipped lens, dust, smudges, fingerprints.
Fixed Pattern Noise (Honeycomb)
This is usually a cosmetic blemish characterized by a faint hexagonal pattern throughout the viewing area that most often at high-light levels or when viewing bright lights. This pattern can be seen in every image intensifier if the light levels are high enough.
Image Disparity
A difference in the brightness between the two image intensifier assemblies within the same binocular
Output Brightness Variation
This condition is evidenced by areas of varying brightness in or across the image area in an individual monocular.
Optimum Sight Adjustment Procedure (OSAP)
To precisely align each monocular to the individual eye by obtaining the optimum sight picture.
- Disregard focus so uniform light can exist across FOV
- Use lighting condition 50-100% moon illumination and relatively uniform background
- Preset all mechanical settings to middle adjustment
- Power ON, look for green glow
- Vertical Adjustment knob so FOV is circular and roughly centered
- Obtain clear edges with eye-span knob
- Fore and aft adjustment away until edges blur
- Once aligned, do 1/2 click inwards to compensate for shifting
Indoor Focus
Focus on object 20’ away until image is clear
Outdoor Focus
Focus on object 125-200’ away until image is clear
Retinal Rivalry
When binocular focus is uneven causing increased eyestrain
Myopia, Hyperopia, Presbyopia
nearsightedness, farsightedness, inability to focus on near objects - no more eye elastic
Illumination
Amount of light that strikes a surface at distance. Footcandle
Luminance
Amount of light per unit of area. Footlamberts
Reflectance
Relationship of illumination reaching the surface and resulting luminance. 100% reflectance would be 1 footcandle to 1 footlambert.
Contrast
Difference in luminance between an object and its background. Positive if object brighter than backgrounds, or negative if object is darker.
