ASTM F1181-19

Standard Test Method for Measuring Binocular Disparity in Transparent Parts

SIGNIFICANCE AND USE
5.1 Diplopia or doubling of vision occurs when there is sufficient binocular disparity present so that the bounds of Panum's area (the area of single vision) is exceeded. This condition arises whenever one object is significantly closer (or farther) than another so that looking at one will cause the image of the other to appear double. This can be easily demonstrated: Close one eye and look at a clock (or other object) on a distant wall. Now place your thumb to one side of the image of the clock. Now open both eyes. If you look at the clock, you should see two thumbs. If you look at your thumb, you should see two clocks.  
5.2 Complaints from pilots flying aircraft equipped with wide field of view head up displays (HUDs), such as the LANTIRN HUD, indicated that they were experiencing discomfort (eye fatigue, headaches, and so forth) or seeing either two targets or two pippers (aiming symbols on the HUD) when using the HUD. Subsequent investigations revealed that the problem arose from the fact that the aircraft transparency and the HUD significantly changed the optical distances of the target and the HUD imagery so that binocular disparity, which exceeded Panum's area was induced. Use of this test method provides a procedure by which the amount of binocular disparity being experienced by a human operator due to the presence of a transparent part in their field of view may be easily and precisely measured.
SCOPE
1.1 This test method covers the amount of binocular disparity that is induced by transparent parts such as aircraft windscreens, canopies, HUD combining glasses, visors, or goggles. This test method may be applied to parts of any size, shape, or thickness, individually or in combination, so as to determine the contribution of each transparent part to the overall binocular disparity present in the total “viewing system” being used by a human operator.  
1.2 This test method represents one of several techniques that are available for measuring binocular disparity, but is the only technique that yields a quantitative figure of merit that can be related to operator visual performance.  
1.3 This test method employs apparatus currently being used in the measurement of optical angular deviation under Test Method F801.  
1.4 The values stated in inches (Imperial units) are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.5 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.  
1.6 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: 31-Oct-2019
• ICS: 17.180.01 - Optics and optical measurements in general
• Technical Committee: F07 - Aerospace and Aircraft
• Drafting Committee: F07.08 - Transparent Enclosures and Materials

Relations

• Replaces: ASTM F1181-09(2014) - Standard Test Method for Measuring Binocular Disparity in Transparent Parts
• Effective Date: 01-Nov-2019
• Refers: ASTM F801-96(2008) - Standard Test Method for Measuring Optical Angular Deviation of Transparent Parts
• Effective Date: 01-Apr-2008
• Refers: ASTM F801-96 - Standard Test Method for Measuring Optical Angular Deviation of Transparent Parts
• Effective Date: 10-Nov-1996
• Refers: ASTM F801-96(2002) - Standard Test Method for Measuring Optical Angular Deviation of Transparent Parts
• Effective Date: 10-Nov-1996
• Referred By: ASTM F790-23 - Standard Guide for Testing Materials for Aerospace Plastic Transparent Enclosures
• Effective Date: 01-Nov-2019
• Referred By: ASTM F2469-20 - Standard Test Method for Measuring Optical Angular Deviation of Transparent Parts Using the Double-Exposure Method
• Effective Date: 01-Nov-2019

Overview

ASTM F1181-19 is the Standard Test Method for Measuring Binocular Disparity in Transparent Parts, developed by ASTM International. This test method provides a quantitative procedure to determine the amount of binocular disparity caused by transparent components, such as aircraft windscreens, canopies, head-up display (HUD) combining glasses, visors, or goggles. Binocular disparity refers to the difference between the images seen by each eye, which can significantly impact visual performance and operator comfort. Excessive disparity in transparent parts may result in diplopia (double vision), eye fatigue, or headaches, especially in high-performance environments like aviation.

Key Topics

• Binocular Disparity: The standard defines methods to measure the difference between the retinal images each eye perceives due to transparent parts within a user’s field of view.
• Impact on Vision: When binocular disparity exceeds the eye’s natural fusion limits (Panum’s area), users may experience double vision and visual discomfort.
• Test Method: Employs optoelectronic apparatus-similar to equipment used in ASTM F801 for optical angular deviation-to take precise, repeatable readings from positions that represent the average interpupillary distance.
• Result Interpretation: The procedure yields values for horizontal and vertical disparity, allowing comparison against operational specifications to ensure transparent parts do not degrade operator visual performance.

Applications

• Aerospace and Defense: The test method is widely used in the evaluation of transparent aircraft components, such as windscreens and HUD combining glasses, where optimal visual performance is critical for safety and mission success.
• Pilot and Operator Safety: Ensuring that transparent parts do not introduce excessive binocular disparity helps prevent issues like diplopia and visual fatigue, which have been reported by pilots using wide field-of-view HUD systems.
• Quality Control: Manufacturers can apply this standard to verify and document conformity of transparent parts at various stages of production, ensuring each component's contribution to the overall viewing system remains within acceptable limits.
• R&D and Product Development: Optical engineers and designers utilize this method when developing new cockpit transparencies, visors, or goggles, facilitating the optimization of designs for human factors and compliance.

Related Standards

• ASTM F801: Standard Test Method for Measuring Optical Angular Deviation of Transparent Parts. ASTM F1181-19 employs similar apparatus and is closely associated with this standard for measuring angular deviation.
• Visual Performance Standards: ASTM F1181-19 provides directly relevant quantitative measurements for compliance with operator visual specifications in aviation and other fields requiring high optical clarity.
• International Principles: Developed in accordance with WTO TBT Committee guidelines, ensuring consistency with globally recognized standardization practices.

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By following ASTM F1181-19, organizations involved in aerospace component design, manufacturing, and testing can ensure transparent parts support safe, comfortable, and effective operator performance. Its quantitative approach provides actionable data for addressing visual quality and meeting rigorous industry requirements for binocular vision and double vision prevention. For further compliance, this test method is best used in conjunction with related optical standards and regulatory specifications.

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: F1181 − 19
Standard Test Method for
Measuring Binocular Disparity in Transparent Parts
This standard is issued under the fixed designation F1181; 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the amount of binocular dispar-
F801 Test Method for Measuring OpticalAngular Deviation
ity that is induced by transparent parts such as aircraft
of Transparent Parts
windscreens, canopies, HUD combining glasses, visors, or
goggles. This test method may be applied to parts of any size,
3. Terminology
shape, or thickness, individually or in combination, so as to
determine the contribution of each transparent part to the 3.1 Definitions:
overall binocular disparity present in the total “viewing sys- 3.1.1 angular deviation, n—the angular displacement of a
light ray as it passes through a transparent part, expressed as an
tem” being used by a human operator.
angular measurement, for example, degree, minutes of arc,
1.2 This test method represents one of several techniques
milliradians.
that are available for measuring binocular disparity, but is the
3.1.1.1 Discussion—Since it is an angular measurement, the
only technique that yields a quantitative figure of merit that can
amount of linear displacement increases with distance.
be related to operator visual performance.
3.1.2 binoculardisparity,n—the difference between the two
1.3 This test method employs apparatus currently being
images on the retina resulting from the lateral separation
used in the measurement of optical angular deviation under
between the two eyes when viewing an object at a fixation
Test Method F801.
point or due to the fact that an object is either nearer or farther
than the fixation point.
1.4 The values stated in inches (Imperial units) are to be
regarded as standard. The values given in parentheses are
3.1.2.1 Discussion—Acertain amount of disparity is benefi-
mathematical conversions to SI units that are provided for
cial and natural, leading to the perception of depth. However,
information only and are not considered standard.
when the disparity exceeds the limits for binocular fusion,
doubling of vision, eye fatigue, and headaches occur as the
1.5 This standard does not purport to address all of the
eyes strain to merge the disparate images.
safety concerns, if any, associated with its use. It is the
3.1.3 diplopia, n—the doubling of images of an object due
responsibility of the user of this standard to establish appro-
to the fact that the object is either nearer or farther than the
priate safety, health, and environmental practices and deter-
point of fixation or due to the fact that the lines of regard of the
mine the applicability of regulatory limitations prior to use.
eyes do not intersect at the point of fixation.
1.6 This international standard was developed in accor-
dance with internationally recognized principles on standard- 3.1.4 Panum’s area, n—the area on the retina in which the
eyes are able to fuse disparate images so that single vision
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom- occurs.
mendations issued by the World Trade Organization Technical
4. Summary of Test Method
Barriers to Trade (TBT) Committee.
4.1 Using an optoelectronic system (consisting of a trans-
mitter and a receiver, described in Test Method F801) and with
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. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Nov. 1, 2019. Published November 2019. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1988. Last previous edition approved in 2014 as F1181 – 09(2014). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/F1181-19. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1181 − 19
the part held in its installed angle, two sets of angular deviation (0.0254 mm). Using this element spacing and the 10 in.
measurements are made at several intervals (for example, 2°) (254 mm) lens, each diode will represent the equivalent of
in both azimuth and elevation. The extent of the area to be 0.1 mrad angular deviation.
measured is dependent on the type of part being measured, for 6.2.4 Electronic System that determines the center diode of
example, windscreen, visor, and so forth. The first set of the band of illuminated diodes on each CCD array.
measures is taken from the left eye position, the second from 6.2.5 Electronic System that converts the number to be
the right eye position. The separation between the two eye displayed on the digital readout.
positions is 2.5 in. (6.35 cm), a distance equivalent to the
6.3 Transmitter and Receiver Lenses shall be of achromatic
interpupillary distance between the human eyes. The measure-
construction to reduce the effect of aberrations on the measure-
ments taken from the left eye position are subtracted from that
ment.
taken from the right eye position to determine binocular
6.4 Dioptomer to verify attainment of collimated light.
disparity.
7. Test Specimen
5. Significance of Use
7.1 Position the part to be tested in such a manner as to
5.1 Diplopia or doubling of vision occurs when there is
approximate its installed configuration. No special condition-
sufficient binocular disparity present so that the bounds of
ing other than cleaning is required.
Panum’s area (the area of single vision) is exceeded. This
condition arises whenever one object is significantly closer (or
8. Procedure
farther)thananothersothatlookingatonewillcausetheimage
of the other to appear double. This can be easily demonstrated:
8.1 Mount the transparent part on a fixture that allows
Close one eye and look at a clock (or other object) on a distant
accurate determination of the elevation and azimuth position of
wall. Now place your thumb to one side of the image of the
the part.
clock. Now open both eyes. If you look at the clock, you
8.2 Locate and firmly mount the receiver at a position
should see two thumbs. If you look at your thumb, you should
corresponding to the design eye position (the cyclopean eye
see two clocks.
position). To obtain the position corresponding to the left
5.2 Complaints from pilots flying aircraft equipped with
(right) eye position, move the transparency 1.25 in.
wide field of view head up displays (HUDs), such as the
(31.75 mm) to the right (left) of the design eye position.
LANTIRN HUD, indicated that they were experiencing dis-
8.3 Locate and firmly mount the transmitter external to the
comfort (eye fatigue, headaches, and so forth) or seeing either
part to be measured and at a distance from the receiver that is
two targets or two pippers (aiming symbols on the HUD) when
commensurate with the part being measured (sufficient to
using the HUD. Subsequent investigations revealed that the
ensure the part being measured will not physically contact the
problem arose from the fact
...

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: F1181 − 09 (Reapproved 2014) F1181 − 19
Standard Test Method for
Measuring Binocular Disparity in Transparent Parts
This standard is issued under the fixed designation F1181; 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
1.1 This test method covers the amount of binocular disparity that is induced by transparent parts such as aircraft windscreens,
canopies, HUD combining glasses, visors, or goggles. This test method may be applied to parts of any size, shape, or thickness,
individually or in combination, so as to determine the contribution of each transparent part to the overall binocular disparity present
in the total “viewing system” being used by a human operator.
1.2 This test method represents one of several techniques that are available for measuring binocular disparity, but is the only
technique that yields a quantitative figure of merit that can be related to operator visual performance.
1.3 This test method employs apparatus currently being used in the measurement of optical angular deviation under Test Method
F801.
1.4 The values stated in inch-pound units inches (Imperial units) are to be regarded as standard. The values given in parentheses
are mathematical conversions to SI units that are provided for information only and are not considered standard.
1.5 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.
1.6 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
2.1 ASTM Standards:
F801 Test Method for Measuring Optical Angular Deviation of Transparent Parts
3. Terminology
3.1 Definitions:
3.1.1 angular deviation—deviation, n—the angular displacement of a light ray as it passes through a transparent part, expressed
as an angular measurement, for example, degree, minutes of arc, milliradians. Since it is an angular measurement, the amount of
linear displacement increases with distance.
3.1.1.1 Discussion—
Since it is an angular measurement, the amount of linear displacement increases with distance.
3.1.2 binocular disparity—disparity, n—the difference between the two images on the retina resulting from the lateral separation
between the two eyes when viewing an object at a fixation point or due to the fact that an object is either nearer or farther than
the fixation point. A certain amount of disparity is beneficial and natural, leading to the perception of depth. However, when the
disparity exceeds the limits for binocular fusion, doubling of vision, eye fatigue, and headaches occur as the eyes strain to merge
the disparate images.
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 Dec. 1, 2014Nov. 1, 2019. Published December 2014November 2019. Originally approved in 1988. Last previous edition approved in 20092014
as F1181 – 09.F1181 – 09(2014). DOI: 10.1520/F1181-09R14.10.1520/F1181-19.
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
F1181 − 19
3.1.2.1 Discussion—
A certain amount of disparity is beneficial and natural, leading to the perception of depth. However, when the disparity exceeds
the limits for binocular fusion, doubling of vision, eye fatigue, and headaches occur as the eyes strain to merge the disparate
images.
3.1.3 diplopia—diplopia, n—the doubling of images of an object due to the fact that the object is either nearer or farther than
the point of fixation or due to the fact that the lines of regard of the eyes do not intersect at the point of fixation.
3.1.4 Panum’s area—area, n—the area on the retina in which the eyes are able to fuse disparate images so that single vision
occurs.
4. Summary of Test Method
4.1 Using an optoelectronic system (consisting of a transmitter and a receiver, described in Test Method F801) and with the part
held in its installed angle, two sets of angular deviation measurements are made at several intervals (for example, 2°) in both
azimuth and elevation. The extent of the area to be measured is dependent on the type of part being measured, for example,
windscreen, visor, and so forth. The first set of measures is taken from the left eye position, the second from the right eye position.
The separation between the two eye positions is 2.5 in. (6.35 cm), a distance equivalent to the interpupillary distance between the
human eyes. The measurements taken from the left eye position are subtracted from that taken from the right eye position to
determine binocular disparity.
5. Significance of Use
5.1 Diplopia or doubling of vision occurs when there is sufficient binocular disparity present so that the bounds of Panum’s area
(the area of single vision) is exceeded. This condition arises whenever one object is significantly closer (or farther) than another
so that looking at one will cause the image of the other to appear double. This can be easily demonstrated: Close one eye and look
at a clock (or other object) on a distant wall. Now place your thumb to one side of the image of the clock. Now open both eyes.
If you look at the clock, you should see two thumbs. If you look at your thumb, you should see two clocks.
5.2 Complaints from pilots flying aircraft equipped with wide field of view head up displays (HUDs)(HUDs), such as the
LANTIRN HUD, indicated that they were experiencing discomfort (eye fatigue, headaches, and so forth.)forth) or seeing either
two targets or two pippers (aiming symbols on the HUD) when using the HUD. Subsequent investigations revealed that the
problem arose from the fact that the aircraft transparency and the HUD significantly changed the optical distances of the target and
the HUD imagery so that binocular disparity, which exceeded Panum’s area was induced. Use of this test method provides a
procedure by which the amount of binocular disparity being experienced by a human operator due to the presence of a transparent
part in histheir field of view may be easily and precisely measured.
6. Apparatus
6.1 Transmitter capable of projecting collimated light rays from a suitable target. The transmitter shouldshall be firmly fixed to
the floor or other stationary fixture.
6.2 Receiver firmly affixed to the floor or a stable platform consisting of the following components:
6.2.1 Displacement Compensation and Imaging Lens with a focal length of 10 in. (254 mm).
6.2.2 Optical Beam Splitter to separate the incoming light into two orthogonal elements (elevation and azimuth). The beam
splitter shouldshall be positioned to keep both optical path lengths equal.
6.2.3 Two Linear Charge Coupled Devices (CCD or diode)Diode) Arrays, each located at the focal plane of the displacement
compensating lens. One array is oriented horizontally (for the measurement of azimuthal changes) and
...