1、Designation: F2469 15Standard 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
2、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 b
3、y 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. Al
4、so, 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 o
5、f 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
6、 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,
7、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 backboa
8、rd 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 te
9、st pattern. A camera 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 measure
10、s 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 ess
11、entially 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 windscr
12、een 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 win
13、dscreen 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 blac
14、k 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
15、 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 pa
16、ge onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16.2 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
17、 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 providesilluminati
18、on of the strings.6.2.1.1 Type 1aThe string board is composed of whitestrings held taut, each spaced at a specific interval, with thestrings stretched horizontally only. The string board frame andbackground shall have a flat black finish to reduce lightreflection. A bank of fluorescent lights at eac
19、h side provideseven illumination of the strings. This can also be used outsideunder natural sunlight conditions.6.2.2 Type 2The grid board is a transparent sheet havingan opaque, flat black outer surface except for the grid lines. Thegrid lines remain transparent, and when backlit with fluores-cent
20、or incandescent lights, provide a bright grid patternagainst a black background with excellent contrast character-istics.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
21、 by theprocuring activity.6.2.4 Type 4The grid board shall have a width and heightlarge enough so that the area of the part to be imaged can besuperimposed within the perimeter of the grid board. Details ofthe grid square size shall be as specified by the procuringagency. The recommended grid line s
22、pacing is not less than1.27 cm (12 in.), or more than 2.54 cm (1 in.).6.3 CameraThe camera is used to photograph opticaldeviation through the transparency using a double-exposuremethod. It is recommended that a large format camera be used,although a high resolution digital camera is acceptable. Thec
23、amera shall be firmly mounted to prevent any movementduring the photographic exposure.7. Test Specimen7.1 The transparency to be measured shall be cleaned usingany acceptable procedure, to remove any foreign material thatmight cause localized optical distortion. No specialconditioning, other than cl
24、eaning, is required. The part shall beat ambient temperature.8. Procedure8.1 Firmly mount the flat transparent part parallel to thesurface of the grid board target pattern at a distance of 450 cm(Setup A, see Fig. 2) or 300 cm (Setup B, see Fig. 2)oratdistance specified by procuring agency.8.2 Mount
25、 the camera a specified distance from the flattransparent part as shown in Fig. 2. This distance is to be550 cm (Setup A) or 450 cm (Setup B) or some other distancespecified by the procuring agency (see Fig. 2). Make sure thatthe optical axis of the camera is perpendicular to the grid boardsurface a
26、nd is aimed at the center of the target panel.FIG. 1 Grid Board PatternF2469 1528.3 Insure that the grid board pattern is in good focus at thefocal plane of the camera. It is suggested that the F-number ofthe camera be set at F/8 or higher (smaller aperture) to improvefocus.8.4 Produce a double-expo
27、sure photograph by photograph-ing the grid board through the transparency and then, withoutallowing any movement of the camera and without advancingthe film, remove the part and take a second exposure of the gridboard alone. Alternatively, if a digital camera is used, the twoexposures (with and with
28、out the flat transparent part in theoptical path) can be superimposed digitally using appropriateimage processing software and all measurements can be madeon the digitally “double-exposed” image.8.5 Develop the film and produce 8 by 10 inch. matte finishprints (minimum size). The matte finish will r
29、educe reflectionproblems during measurement. Alternatively, use the “double-exposed” digital image described above.8.6 The double-exposure photograph (digital image) is ex-amined to locate the area of maximum grid line shift (betweenexposures) in either the horizontal or vertical direction (seeFig.
30、3).FIG. 2 Suggested Distances for Measurements.FIG. 3 Example of Double-Exposure Measurement of Optical DeviationF2469 1538.7 Measure the maximum grid shift from the true grid linein centimeters (or digital units if a digital image is used) andcalculate deviation according to 9.1.9. Calculations9.1
31、Each grid square as photographed represents a specificangular significance, therefore:Angular deviation 5 5 S 3 G/T (1)where: = angular deviation in milliradians,S = grid significance in milliradians (the angular subtense ofone grid square),G = grid shift as measured on the photograph, cm (or digita
32、lunits if digital camera is used) andT = true (undistorted not imaged through the transparency)grid dimension (i.e., the size of a side of one square ofthe grid pattern) as measured on the photograph (cm) ordigital image (SAME digital units as used to measure Gabove).The grid significance, S, is cal
33、culated using the followingequation:Grid significance 5 S 5 1000 3 D/P! (2)where:S = grid significance,D = actual grid dimension in cm (for example, 2.54 cm), andP = part-to-grid-board distance in cm.In order that angular deviation be in units of milliradians,grid significance S must be in milliradi
34、ans. Grid significance Sis a nominally unitless parameter, insofar as actual griddimension D and part-to-grid-board distance P must be in thesame length units. A physical interpretation of the ratio D/P inEq 2 is the tangent of the angle subtended at the part (of lengthP from the grid board) by the
35、actual grid dimension (of lengthD). For angle sizes of 0.114 radians or less, angle size inradians is equivalent to the numerical value of the tangent ofthe angle (to three decimal places). So it is that the ratio D/Prepresents the subtended angle in radians for angles of0.114 radians or less (an an
36、gle range which fully covers thescope of this standard). The multiplier of 1000 in Eq 2 convertsradians to milliradians, thereby placing grid significance S inmilliradians, as required for angular deviation to be in unitsof milliradians.10. Precision and Bias10.1 Precision and bias has not yet been
37、determined for thistest method. The subcommittee is in process of planning anInterlaboratory Study to collect data for this section.11. Keywords11.1 angular deviation; canopy; grid board; optical devia-tion; transparencyASTM International takes no position respecting the validity of any patent right
38、s asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any t
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