ASTM F2429-15(2021)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F2429 − 15 (Reapproved 2021)
Standard Terminology Relating to
Aerospace Transparent Materials and Enclosures
This standard is issued under the fixed designation F2429; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope which have been known to appear in transparencies as
rainbowing or the apparent random dispersion of light into
1.1 These definitions cover generic optical terms which
its component colors.
appear in one of more standards relating to aerospace trans-
parent materials and enclosures.
crazing—theoccurrenceofverysmall,localized,micro-cracks
at or under the surface of, but not extending entirely through,
1.2 The definitions cover, in most cases, special meanings
a transparent material, which act like tiny mirrors that reflect
used in the transparency industry. No attempt has been made to
light in unwanted directions.
includecommonmeaningsofthesametermsasusedoutsideof
the transparency industry.
design eye—the reference point in aircraft design from which
1.3 Definitions included have, in general, been approved as all visual or optical anthropometrical design considerations
standard. are taken.
1.4 This international standard was developed in accor-
distortion—the rate of change of angular deviation across the
dance with internationally recognized principles on standard-
transparency, usually characterized by grid-line slope, result-
ization established in the Decision on Principles for the
ing in the non-linear mapping of objects viewed through the
Development of International Standards, Guides and Recom-
transparency.
mendations issued by the World Trade Organization Technical
grid line slope—anopticaldistortionevaluationparameterthat
Barriers to Trade (TBT) Committee.
compares the slope of a deviated grid line to that of a
2. Terminology
non-deviated grid line, which is expressed as a ratio such as
1 in 8 or 1 in 20 (the visual optical quality improves as the
2.1 Definitions:
second number of the ratio gets larger).
angular deviation—the angular displacement of a light ray
from its original path caused by non-parallelism of opposite
halation—the scattering of light by the transparency into the
surfaces as it passes through a transparent material, which is
viewer’s line-of-sight reducing the perceived contrast of
expressed in units of angle (degree, minutes of arc, millira-
external objects, also referred to as haze.
dians) and is a function of the angle of incidence at each
haze—the percent of transmitted light that is scattered so that
surface of the material and the index of refraction of the
its direction deviates more than a specified angle from the
material.
direction of the incident beam, resulting in the reduction of
angular displacement—the angular separation of the second-
contrast of objects viewed through the transparency.
ary image from the primary image as measured from the
multiple imaging separation—the angular separation of pri-
design eye position of a transparency.
mary and secondary multiple images as measured from the
binocular disparity—the difference in angular deviation be-
design eye position.
tween two light rays passing
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