Helmet-Mounted Displays: - USAARL - The - U.S. Army

HMD Terms
Aberration: Any variance from a perfect reproduction of an image.
Accommodation: The process by which the focal length of the eye’s lens
is changed so that images of objects viewed at any distance are focused on
the retina.
Achromats: A combination of lenses (usually in contact) which reduce
chromatic aberration.
Active matrix liquid crystal display (AMLCD): A type of liquid crystal
display which employs an array of individual pixels, each controlled by an
electronic switch.
Active noise reduction (ANR): A technique that uses counterphase
cancellation to manipulate and reduce noises within the earcup.
Aircraft retained unit (ARU): The frontal portion of the Helmet
Integrated Display Sight System (HIDSS), consisting of two image sources,
and optical relays attached to a mounting bracket.
Aspect ratio: The ratio of width to height.
Astigmatic aberration: Aberration due to the irregular curvature of the
ocular surface resulting in unequal refraction of the incident light in
different meridians.
Aviator’s night vision imaging system (ANVIS): A passive, binocular,
third generation I 2 system with improved sensitivity and resolution over the
second generation I 2 tubes: ANVIS are used extensively in Army aviation.
Bandwidth: The gamut of frequencies over which a device performs within
specified limits.
Biocular display: A term pertaining to optical devices which provide two
visual inputs from a single sensor.
Binocular alignment: The condition by which the optical axes of two
independent oculars are parallel.
Binocular display: A term pertaining to optical devices which provide two
visual inputs from two sensors which are displaced horizontally in space,
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