ASTM F801-21

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. Both parameters are illustrated in Fig. X1.1.
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 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.3 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.

General Information

• Status: Published
• Publication Date: 30-Apr-2021
• ICS: 49.035 - Components for aerospace construction
• Technical Committee: F07 - Aerospace and Aircraft
• Drafting Committee: F07.08 - Transparent Enclosures and Materials

Standards Content (Sample)

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: F801 − 21
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 change in angle of such a light ray. The displacement of an
image due to the change in direction of the light ray.
1.1 Thistestmethodcoversmeasuringtheangulardeviation
3.1.2 lateral (or linear) displacement, n—the shift or move-
of a light ray imposed by transparent parts such as aircraft
ment of a light ray from its original path as it passes through a
windscreens and canopies. The results are uncontaminated by
transparent material, while maintaining parallelism between
the effects of lateral displacement, and it is possible to perform
the original and final paths.The change in location of an image
the procedure in a relatively short optical path length. This is
due to this change in path.
not intended as a referee standard. It is one convenient method
formeasuringangulardeviationsthroughtransparentwindows.
3.1.3 modulation transfer function (MTF), n—the ratio of
output modulation to the input modulation.The modulus of the
1.2 This standard does not purport to address all of the
Fourier transform of the optical spread function.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
4. Summary of Test Method
priate safety, health, and environmental practices and deter-
4.1 This test method provides a basic procedure for mea-
mine the applicability of regulatory limitations prior to use.
1.3 This international standard was developed in accor- suring the angular deviation induced by a transparent part.
Angular deviation measurements are made by an optoelec-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the tronic system employing collimated light from an appropriate
target pattern, a field lens, and a position-detecting device/
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical system such as linear diode arrays or a two-dimensional diode
array. Hold the transparent part either in its installed angle or
Barriers to Trade (TBT) Committee.
perpendicular to the collimated light source or any other
2. Referenced Documents
orientation suitable for the purpose of making the measure-
2
2.1 ASTM Standards: ment. One specific optoelectronic system suitable for conduct-
ing this test method is provided in Appendix X2 and Appendix
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method X3 and in Section 6 below.
F733 Practice for Optical Distortion and Deviation ofTrans-
5. Significance and Use
parent Parts Using the Double-Exposure Method
F2156 Test Method for Measuring Optical Distortion in 5.1 One of the measures of optical quality of a transparent
Transparent Parts Using Grid Line Slope
part is its angular deviation. It is possible that excessive
angulardeviation,orvariationsinangulardeviationthroughout
3. Terminology
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, n—thedepartureofalightrayfrom ficationareofextremeimportanceintheareaofcertainaircraft
its original path as it passes through a transparent material.The 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
1
This test method is under the jurisdiction of ASTM Committee F07 on
transparency (windscreen or canopy) which lies between the
Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on
Transparent Enclosures and Materials.
HUD combining glass and the external environment. Military
Current edition approved May 1, 2021. Published June 2021. Originally
aircraft equipped with HUDs or similar devices require precise
approved in 1983. Last previous edition approved in 2016 as F801 – 16. DOI:
knowledgeoftheeffectsofthewindscreenorcanopyonimage
10.1520/F0801-21.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or position in order to maintain weapons aiming accuracy.
contact ASTM Customer Servi
...

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 − 16 F801 − 21
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 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.3 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.
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
F2156 Test Method for Measuring Optical Distortion in Transparent Parts Using Grid Line Slope
3. Terminology
3.1 Definitions:
3.1.1 angular deviation—deviation, n—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,—n—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.
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, 2016May 1, 2021. Published April 2016June 2021. Originally approved in 1983. Last previous edition approved in 20082016 as
F801 – 96 (2008).F801 – 16. DOI: 10.1520/F0801-16.10.1520/F0801-21.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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 − 21
3.1.3 modulation transfer function (MTF)—), n—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 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 from an appropriate target pattern, a
field lens, and a position-detecting device/system such as linear diode arrays or a two-dimensional diode array. Hold the transparent
part either in its installed angle or perpendicular to the collimated light source or 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 and in Section 6 below.
5. 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 ang
...