Autogating
Autogating rapidly turns the power supply on and off to limit light exposure to the photocathode, preserving image quality in bright or fluctuating light. Without it, images can degrade and become "bloomed," making peripheral subjects hard to discern.
Automatic Brightness Control (Auto-Gain)
This feature adjusts microchannel plate voltages to maintain optimal brightness levels, ensuring the image stabilizes quickly when transitioning from low to high light.
Biocular vs. Binocular
A biocular system, like the PVS-7, has one objective lens and two ocular lenses for both eyes, while a binocular system, such as RNVGs, features separate optics for each eye.
Black Spots/Dark Spots ("Blems")
Dark spots can be factory defects or user-induced blemishes from high-intensity light sources. Factory spots are often fuzzy with lighter rings, while user blemishes may be irregular and arise from debris.
Blooming
Blooming occurs when bright light overloads the intensifier, causing parts or the entirety of the night vision image to "whiten" or become obscured, commonly seen in earlier generations.
Bright Spots
These are small bright defects in the image caused by microchannel plate flaws, often temporary and cosmetic.
Bright Spot Protection (BSP)
BSP automatically reduces photocathode voltage under bright light to protect the image tube, though it may lower resolution.
Fixed Pattern Noise
This appears as dark lines in high light conditions, often in a honeycomb pattern, but is usually not a concern in low light.
Daylight Cover/Day Cap
A soft cap with a pinhole, meant for training, that allows minimal light in; not suitable for extended use.
Diopter
This unit measures lens refractive power for users eye correction, typically adjustable between +2 to -6.
Distortion
Optical distortion can arise from design flaws or manufacturing defects, affecting the straightness of lines in the image.
Edge Glow
A bright area at the edge of the view, which can be minimized with a rubber eyecup but may reduce peripheral awareness.
Emission Point
A persistent bright spot in the image that requires repair if it remains visible under all lighting conditions.
Equivalent Background Illumination (EBI)
The light visible when the night vision device is on without any external illumination; lower values are better.
Eye Relief
The optimal distance from the eyepiece for clear viewing, typically around 35mm for comfort. The longer eye relief, the better. Generally, wide FOV lenses have a shorter eye relief.
Field of View (FOV)
The diameter of the visible area through the optic.
Figure of Merit (FOM)
A performance metric calculated from resolution (lp/mm) and signal-to-noise ratio.
Fixed Pattern Noise
A faint hexagonal pattern often seen in bright conditions, characteristic of Gen 2 and 3 systems.
Gain
Light amplification measured as tube gain and system gain, with military Gen 3 tubes typically operating between 20,000 and 30,000, and Gen 2 tubes between 9,000 and and 15,000.
Gallium Arsenide (GaAs)
A highly sensitive semiconductor used in Gen 3 photocathodes, enhancing performance in low light. In Gen 2 multi-alkali photocathodes are used,
Generations of Night Vision
Night vision devices are classified into four generations, with Gen 0 to Gen 3.
Highlight Shutoff
This feature protects image intensifiers by turning them off during extreme brightness.
I² (Image Intensification)
A process that amplifies light in visible and near-infrared spectra for clearer low-light images.
Interpupillary Adjustment
Adjusts binocular optics to align with the user’s eye distance for proper viewing.
Infrared Light
Invisible light used for night vision, emitted by IR illuminators to enhance image contrast.
Lp/mm (Line Pair per Millimeter)
A resolution measure for image intensifiers, indicating the ability to distinguish close objects.
MCP (Microchannel Plate)
A component in Gen 2 and 3 systems that multiplies electrons, enhancing resolution.
Monocular
A single-tube night vision device, like the PVS-14.
Photocathode
The surface in an image intensifier that converts light to electrical signals, differing by generation.
Resolution
The ability to distinguish objects in an image, measured in lp/mm for intensifiers.
Signal to Noise Ratio (SNR)
A performance indicator relating to image clarity in low light; higher values indicate better performance. Ranges generally from 20 to 25.
Stereoscopic Night Vision
Captures separate images for each eye, creating a depth perception effect when viewed together.
System Gain
Total gain after accounting for losses from lenses and filters, critical for user experience.
Variable Gain Control
Unlike Auto-Gain, variable gain requires manual adjustment of gain in varying light conditions.