ASTM_F_801_-_16.pdf

Designation:F80116Standard Test Method forMeasuring Optical Angular Deviation of Transparent Parts1This standard is issued under the fixed designation F801;the number immediately following the designation indicates the year of originaladoption or,in the case of revision,the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon()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.Scope1.1 This test method covers measuring the angular deviationof a light ray imposed by transparent parts such as aircraftwindscreens and canopies.The results are uncontaminated bythe effects of lateral displacement,and it is possible to performthe procedure in a relatively short optical path length.This isnot intended as a referee standard.It is one convenient methodfor measuring angular deviations through transparent windows.1.2 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:2E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodF2156 Test Method for Measuring Optical Distortion inTransparent Parts Using Grid Line SlopeF733 Practice for Optical Distortion and Deviation of Trans-parent Parts Using the Double-Exposure Method3.Terminology3.1 Definitions:3.1.1 angular deviationthe departure of a light ray fromits original path as it passes through a transparent material.Thechange in angle of such a light ray.The displacement of animage due to the change in direction of the light ray.3.1.2 lateral(or linear)displacementthe shift or move-ment of a light ray from its original path as it passes through atransparent material,while maintaining parallelism betweenthe original and final paths.The change in location of an imagedue to this change in path.3.1.3 modulation transfer function(MTF)the ratio ofoutput modulation to the input modulation.The modulus of theFourier transform of the optical spread function.4.Summary of Test Method4.1 This test method provides a basic procedure for mea-suring the angular deviation induced by a transparent part.Angular deviation measurements are made by an optoelec-tronic system employing collimated light from an appropriatetarget pattern,a field lens,and a position-detecting device/system such as linear diode arrays or a two-dimensional diodearray.Hold the transparent part either in its installed angle orperpendicular to the collimated light source or any otherorientation suitable for the purpose of making the measure-ment.One specific optoelectronic system suitable for conduct-ing this test method is provided in Appendix X2 and AppendixX3 and in Section 6 below.5.Significance and Use5.1 One of the measures of optical quality of a transparentpart is its angular deviation.It is possible that excessiveangular deviation,or variations in angular deviation throughoutthe part,will result in visible distortion of scenes viewedthrough the part.Angular deviation,its detection,and quanti-fication are of extreme importance in the area of certain aircrafttransparency applications,that is,aircraft equipped withHeads-up Displays(HUD).It is possible that HUDs willrequire stringent control over the optics of the portion of thetransparency(windscreen or canopy)which lies between theHUD combining glass and the external environment.Militaryaircraft equipped with HUDs or similar devices require preciseknowledge of the effects of the windscreen or canopy on imageposition in order to maintain weapons aiming accuracy.5.2 Two optical parameters have the effect of changingimage position.The first,lateral displacement,is inherent inany transparency which is tilted with respect to the line ofsight.The effect of lateral displacement is constant overdistance,and seldom exceeds a fraction of an inch.The secondparameter,angular deviation,is usually caused by a wedginessor nonparallelism of the transparency surfaces.The effect of1This 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 April 1,2016.Published April 2016.Originallyapproved in 1983.Last previous edition approved in 2008 as F801 96(2008).DOI:10.1520/F0801-16.2For 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 angular deviation is related to the tangent of the angle ofdeviation,thu