ASTM F801-16
(Test Method)Standard Test Method for Measuring Optical Angular Deviation of Transparent Parts
Standard Test Method for Measuring Optical Angular Deviation of Transparent Parts
SIGNIFICANCE AND USE
5.1 One of the measures of optical quality of a transparent part is its angular deviation. It is possible that excessive angular deviation, or variations in angular deviation throughout the part, will result in visible distortion of scenes viewed through the part. Angular deviation, its detection, and quantification are of extreme importance in the area of certain aircraft transparency applications, that is, aircraft equipped with Heads-up Displays (HUD). It is possible that HUDs will require stringent control over the optics of the portion of the transparency (windscreen or canopy) which lies between the HUD combining glass and the external environment. Military aircraft equipped with HUDs or similar devices require precise knowledge of the effects of the windscreen or canopy on image position in order to maintain weapons aiming accuracy.
5.2 Two optical parameters have the effect of changing image position. The first, lateral displacement, is inherent in any transparency which is tilted with respect to the line of sight. The effect of lateral displacement is constant over distance, and seldom exceeds a fraction of an inch. The second parameter, angular deviation, is usually caused by a wedginess or nonparallelism of the transparency surfaces. The effect of angular deviation is related to the tangent of the angle of deviation, thus the magnitude of the image position displacement increases as does the distance between image and transparency. The quantification of angular deviation is then the more critical of the two parameters.
SCOPE
1.1 This test method covers measuring the angular deviation of a light ray imposed by transparent parts such as aircraft windscreens and canopies. The results are uncontaminated by the effects of lateral displacement, and it is possible to perform the procedure in a relatively short optical path length. This is not intended as a referee standard. It is one convenient method for measuring angular deviations through transparent windows.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Designation: F801 − 16
Standard Test Method for
1
Measuring Optical Angular Deviation of Transparent Parts
ThisstandardisissuedunderthefixeddesignationF801;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope the original and final paths.The change in location of an image
due to this change in path.
1.1 Thistestmethodcoversmeasuringtheangulardeviation
3.1.3 modulation transfer function (MTF)—the ratio of
of a light ray imposed by transparent parts such as aircraft
output modulation to the input modulation.The modulus of the
windscreens and canopies. The results are uncontaminated by
Fourier transform of the optical spread function.
the effects of lateral displacement, and it is possible to perform
the procedure in a relatively short optical path length. This is
4. Summary of Test Method
not intended as a referee standard. It is one convenient method
formeasuringangulardeviationsthroughtransparentwindows.
4.1 This test method provides a basic procedure for mea-
suring the angular deviation induced by a transparent part.
1.2 This standard does not purport to address all of the
Angular deviation measurements are made by an optoelec-
safety concerns, if any, associated with its use. It is the
tronic system employing collimated light from an appropriate
responsibility of the user of this standard to establish appro-
target pattern, a field lens, and a position-detecting device/
priate safety and health practices and determine the applica-
system such as linear diode arrays or a two-dimensional diode
bility of regulatory limitations prior to use.
array. Hold the transparent part either in its installed angle or
2. Referenced Documents perpendicular to the collimated light source or any other
2 orientation suitable for the purpose of making the measure-
2.1 ASTM Standards:
ment. One specific optoelectronic system suitable for conduct-
E691 Practice for Conducting an Interlaboratory Study to
ing this test method is provided in Appendix X2 and Appendix
Determine the Precision of a Test Method
X3 and in Section 6 below.
F2156 Test Method for Measuring Optical Distortion in
Transparent Parts Using Grid Line Slope
5. Significance and Use
F733 Practice for Optical Distortion and Deviation ofTrans-
5.1 One of the measures of optical quality of a transparent
parent Parts Using the Double-Exposure Method
part is its angular deviation. It is possible that excessive
3. Terminology
angulardeviation,orvariationsinangulardeviationthroughout
the part, will result in visible distortion of scenes viewed
3.1 Definitions:
through the part. Angular deviation, its detection, and quanti-
3.1.1 angular deviation—the departure of a light ray from
ficationareofextremeimportanceintheareaofcertainaircraft
its original path as it passes through a transparent material.The
transparency applications, that is, aircraft equipped with
change in angle of such a light ray. The displacement of an
Heads-up Displays (HUD). It is possible that HUDs will
image due to the change in direction of the light ray.
require stringent control over the optics of the portion of the
3.1.2 lateral (or linear) displacement—the shift or move-
transparency (windscreen or canopy) which lies between the
ment of a light ray from its original path as it passes through a
HUD combining glass and the external environment. Military
transparent material, while maintaining parallelism between
aircraft equipped with HUDs or similar devices require precise
knowledgeoftheeffectsofthewindscreenorcanopyonimage
position in order to maintain weapons aiming accuracy.
1
This test method is under the jurisdiction of ASTM Committee F07 on
Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on
5.2 Two optical parameters have the effect of changing
Transparent Enclosures and Materials.
image position. The first, lateral displacement, is inherent in
Current edition approved April 1, 2016. Published April 2016. Originally
any transparency which is tilted with respect to the line of
approved in 1983. Last previous edition approved in 2008 as F801 – 96 (2008).
DOI: 10.1520/F0801-16.
sight. The effect of lateral displacement is constant over
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
distance, and seldom exceeds a fraction of an inch.The second
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
parameter, angular deviation, is usually caused by a wedginess
Standards volume information, refer to the standard’s Document Summary page on
the A
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F801 − 96 (Reapproved 2008) F801 − 16
Standard Test Method for
1
Measuring Optical Angular Deviation of Transparent Parts
This standard is issued under the fixed designation F801; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This test method covers measuring the angular deviation of a light ray imposed by transparent parts such as aircraft
windscreens and canopies. The results are uncontaminated by the effects of lateral displacement, and the procedure may be
performed it is possible to perform the procedure in a relatively short optical path length. This is not intended as a referee standard.
It is one convenient method for measuring angular deviations through transparent windows.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2
2.1 ASTM Standards:
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
F2156 Test Method for Measuring Optical Distortion in Transparent Parts Using Grid Line Slope
F733 Practice for Optical Distortion and Deviation of Transparent Parts Using the Double-Exposure Method
3. Terminology
3.1 Definitions:
3.1.1 angular deviation—the departure of a light ray from its original path as it passes through a transparent material. The
change in angle of such a light ray. The displacement of an image due to the change in direction of the light ray.
3.1.2 lateral (or linear) displacement—the shift or movement of a light ray from its original path as it passes through a
transparent material, while maintaining parallelism between the original and final paths. The change in location of an image due
to this change in path.
3.1.3 modulation transfer function (MTF)—the ratio of output modulation to the input modulation. The modulus of the Fourier
transform of the optical spread function.
4. Summary of Test Method
4.1 This test method outlines how measurements can be provides a basic procedure for measuring the angular deviation induced
by a transparent part. Angular deviation measurements are made by an optoelectronic system employing collimated light, light
from an appropriate target pattern, a field lens, and a position-detecting device/system such as linear diode arrays as the part is held
or a two-dimensional diode array. Hold the transparent part either in its installed angle. The positions of two images of a angle
or perpendicular to the collimated light source are recorded using two linear diode arrays. One array records azimuth or horizontal
position while the other records elevation or vertical position. These arrays are at the posterior focal plane of a field lens. The
positions are again recorded after the interposition of a transparent part in the optical path. The difference in image position is
directly related toor any other orientation suitable for the purpose of making the measurement. One specific optoelectronic system
suitable for conducting this test method is provided in Appendix X2 and Appendix X3 the angular deviation imposed by the
1
This test method is under the jurisdiction of ASTM Committee F07 on Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on Transparent
Enclosures and Materials.
Current edition approved April 1, 2008April 1, 2016. Published April 2008April 2016. Originally approved in 1983. Last previous edition approved in 20022008 as
F801 – 96 (2002).(2008). DOI: 10.1520/F0801-96R08.10.1520/F0801-16.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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F801 − 16
transparent part. The effects of lateral displacement are removed by the field lens. Sensitivity of measurement may be c
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