ASTM_F_2469_-_15.pdf

Designation:F246915Standard Test Method forMeasuring Optical Angular Deviation of Transparent PartsUsing the Double-Exposure Method1This standard is issued under the fixed designation F2469;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the measurement of the opticalangular deviation of a light ray imposed by flat transparentparts such as a commercial or military aircraft windshield,canopy,or cabin window.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.2.1 ExceptionsThe values given in parentheses are forinformation only.Also,print size is provided in inch-poundmeasurements.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2F801 Test Method for Measuring Optical Angular Deviationof Transparent PartsF1181 Test Method for Measuring Binocular Disparity inTransparent PartsF733 Practice for Optical Distortion and Deviation of Trans-parent Parts Using the Double-Exposure Method3.Terminology3.1 Definitions:3.1.1 angular deviationthe angular displacement of a lightray from its original path caused by non-parallelism of oppositesurfaces as it passes through a transparent material,which isexpressed in units of angle(degree,minutes of arc,milliradi-ans)and is a function of the angle of incidence at each surfaceof the material and the index of refraction of the material.3.1.2 grid boardan optical evaluation tool used to detectthe presence of distortion in transparent parts.It is usually,butnot always,a vertical rectangular backboard with horizontaland vertical intersecting lines with maximum contrast betweenthe white lines and the black background.4.Summary of Test Method4.1 The flat transparent part is mounted at a specifieddistance from a grid board test pattern with its surface parallelwith the plane of the grid board test pattern.Acamera is placedso as to record a double exposure photograph of the gridpattern as viewed through the transparency from a specifiedviewing distance from the grid board test pattern.The image isthen measured to assess the level of optical deviation present.This method basically measures the amount of angular devia-tion present in a flat transparent part when viewing through itperpendicular to its surface.The part to be measured must beessentially flat and mounted such that its surface is perpendicu-lar to the camera axis.This is an alternate method to TestMethod F801 and is essentially the same as the portion ofPractice F733 that deals with optical deviation.5.Significance and Use5.1 The optical angular deviation of flat transparent parts,such as aircraft windshields,canopies,cabin windows,andvisors,can be measured using these methods.Angular devia-tion in a windscreen or visor can cause objects to appear at alocation different from where they actually are.Variations inangular deviation can be used to characterize distortion andmagnification in transparent parts.Also,angular deviationmeasurements made from the typical right and left eye posi-tions for a windscreen or other transparent medium can be usedto determine binocular disparity differences(see Test MethodF1181).6.Apparatus6.1 Test RoomThe test room must be large enough toproperly locate the required testing equipment.6.1.1 The walls,ceiling,and floor shall have low reflec-tance.A flat black paint or coating is preferred.1This test method is under the jurisdiction of ASTM Committee F07 onAerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 onTransparent Enclosures and Materials.Current edition approved Nov.1,2015.Published November 2015.Originallyapproved in 2005.Last previous edition approved in 2010 as F2469 10.DOI:10.1520/F2469-15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.2 Grid BoardThe grid board provides a defined patternagainst which the transparent part is examined(see Fig.1).Grid boards are of the following types:6.2.1 Type 1The grid board is composed of white stringsheld taut,each spaced at a specific interval,with the stringsstretched vertically and horizontally.The grid board frame andbackground shall have a flat black finish to reduce lightreflection.A bank of fluorescent lights