ASTM_F_733_-_09_2014.pdf

Designation:F73309(Reapproved 2014)Standard Practice forOptical Distortion and Deviation of Transparent Parts Usingthe Double-Exposure Method1This standard is issued under the fixed designation F733;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.1.Scope1.1 This photographic practice determines the optical dis-tortion and deviation of a line of sight through a simpletransparent part,such as a commercial aircraft windshield or acabin window.This practice applies to essentially flat or nearlyflat parts and may not be suitable for highly curved materials.1.2 Test Method F801 addresses optical deviation(angluardeviation)and Test Method F2156 addresses optical distortionusing grid line slope.These test methods should be usedinstead of Practice F733 whenever practical.1.3 This standard does not purport to address the safetyconcerns associated with its use.It is the responsibility of theuser of this standard to establish appropriate safety and healthpractices and determine the applicability of regulatory limita-tions prior to use.2.Referenced Documents2.1 ASTM Standards:F801 Test Method for Measuring Optical Angular Deviationof Transparent PartsF2156 Test Method for Measuring Optical Distortion inTransparent Parts Using Grid Line Slope3.Terminology3.1 Definitions:3.1.1 deviationthe displacement of a line or object whenviewed through the transparent part.Expressed as the angularmeasurement of the displaced line,for example,milliradians ofangle.3.1.2 distortionthe rate of change of deviation resultingfrom an irregularity in a transparent part.3.1.3 Expressed as the angular bending of the light ray perunit of length of the part,for example,milliradians percentimetre.3.1.4 May also be expressed as the slope of the angle oflocalized grid line bending,for example,1 in 5(see Fig.1).3.1.5 installed anglethe part attitude as installed in theaircraft.Defined by the angle between a horizontal line and theplane of the part,and the angle of sweep back from a horizontalline normal to the center line of the aircraft.See Fig.2 for anexample.4.Summary of Practice4.1 The transparent part is placed a given distance from agrid line pattern.A camera is placed so as to photograph thegrid pattern as viewed through the part.The photograph is thenexamined and optical distortion or deviation is measured.5.Significance and Use5.1 Transparent parts,such as aircraft windshields andwindows,can be inspected using this practice,and the amountof optical distortion or deviation can be measured.Themeasurement can be checked for acceptability against thespecification for the part.The photograph(digital file,print ornegative)can be maintained as a permanent record of theoptical quality of the part.6.Apparatus6.1 Test RoomThe test room must be large enough toproperly locate the required testing equipment.6.1.1 Method A requires a room approximately 12 m(40 ft)long.6.1.2 Method B requires a room approximately 7 m(23 ft)long.6.1.3 The walls,ceiling,and floor shall have low reflec-tance.A flat black paint or coating is preferred.6.2 Grid BoardThe grid board provides a defined patternagainst which the transparent part is examined.Grid boards areof 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 at each side providesillumination of the strings.1This practice is under the jurisdiction of ASTM Committee F07 on Aerospaceand Aircraft and is the direct responsibility of Subcommittee F07.08 on TransparentEnclosures and Materials.Current edition approved Dec.1,2014.Published December 2014.Originallyapproved in 1981.Last previous edition approved in 2009 as F733 09.DOI:10.1520/F0733-09R14.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.2.2 Type 2The grid board is a transparent sheet havingan opaque,flat black outer surface except for the grid lines.Thegrid lines are left transparent,and when lighted from behindwith fluorescent lights,provide a bright grid pattern withexcellent photographic characteristics.6.2.3 Type 3The grid board is a rigid sheet of materialwhich has a grid pattern printed on the front surface.Details ofthe grid lines,pattern,and lighting shall be as specified by theprocuring activity.6.2.4 The grid board shall have a width and height largeenough so that the area of the part to be photographed can besuperimposed within the perimeter of the grid board.Details ofthe grid square size shall be as specified by the procuringactivity,but grids shall not have a line spacing less than 1.27cm(12in.),or more than