1、Designation: F2469 10Standard 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. Als
4、o, 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
5、 regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2F801 Test Method for Measuring OpticalAngular Deviationof Transparent PartsF1181 Test Method for Measuring Binocular Disparity inTransparent PartsF733 Practice for Optical Distortion and Deviation ofTransparent Parts Usi
6、ng the Double-Exposure Method3. Terminology3.1 Definitions:3.1.1 angular deviationthe angular displacement of alight ray from its original path caused by non-parallelism ofopposite surfaces as it passes through a transparent material,which is expressed in units of angle (degree, minutes of arc,milli
7、radians) and is a function of the angle of incidence at eachsurface of the material and the index of refraction of thematerial.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
8、 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 patt
9、ern. 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 measures the a
10、mount 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 essentiall
11、y 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
12、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
13、 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.1This test method is under the jurisdiction of ASTM Committee F07 onAerospace and A
14、ircraft and is the direct responsibility of Subcommittee F07.08 onTransparent Enclosures and Materials.Current edition approved May 1, 2010. Published June 2010. Originallyapproved in 2005. Last previous edition approved in 2005 as F2469 05. DOI:10.1520/F2469-10.2For referenced ASTM standards, visit
15、 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-295
16、9, United States.6.1.1 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 (see Fig. 1).Grid boards are of the following types:6.2.1 Type 1The grid
17、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 s
18、trings.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 each side prov
19、ideseven 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 or incandes
20、cent 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 by theproc
21、uring 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 spacing is n
22、ot 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. Thecamera shall
23、 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 special condition-ing, other than cleaning, i
24、s required. The part shall be atambient 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 the came
25、ra a specified distance from the flattransparent part as shown in Fig. 2. This distance should be 550cm (Setup A) or 450 cm (Setup B) or some other distanceFIG. 1 Grid Board PatternF2469 102specified by the procuring agency (see Fig. 2). Make sure thatthe optical axis of the camera is perpendicular
26、to the grid boardsurface and is aimed at the center of the target panel.8.3 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-exposure pho
27、tograph 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 without the
28、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 reduce re
29、flectionproblems 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. 3).FIG.
30、2 Suggested Distances for Measurements.FIG. 3 Example of Double-Exposure Measurement of Optical DeviationF2469 1038.7 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 Each gri
31、d square as photographed represents a specificangular significance, therefore:Angular deviation 5a5S 3 G/T (1)where:a = angular deviation in milliradians,S = grid significance in milliradians (the angular subtenseof one grid square),G = grid shift as measured on the photograph, cm (ordigital units i
32、f digital camera is used) andT = true (undistorted not imaged through the transpar-ency) grid dimension (i.e., the size of a side of onesquare of the grid pattern) as measured on the photo-graph (cm) or digital image (SAME digital units asused to measure G above).The grid significance, S, is calcula
33、ted 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.10. Precision and Bias10.1 Precision and bias has not yet been determined for thistest method. The subcom
34、mittee 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 rights asserted in connection with any item men
35、tionedin 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 time by the responsible technical committee
36、 and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meetin
37、g of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO
38、Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).F2469 104
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