1、Designation: F733 09 (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 th
2、e 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 s
3、ight 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 F215
4、6 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 sa
5、fety 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 Lin
6、e 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
7、 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 at
8、titude 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
9、 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 th
10、is 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. Apparatus
11、6.1 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 pa
12、int 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 ver
13、tically 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 AerospaceandAircraft and is the direc
14、t 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, P
15、O Box C700, West Conshohocken, PA 19428-2959. United States16.2.2 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 wi
16、thexcellent 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 lar
17、geenough 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 (12 in.), or more than 2.54 cm (1 in.).6.3 Camer
18、aUnless otherwise specified, the camera shallutilizea4by5-in. film size. The lens opening used shall be f 8or smaller. The camera shall be firmly mounted to prevent anymovement during the photographic exposure. Digital camerasare acceptable if they have sufficient resolution (pixel count)for the siz
19、e of part to be measured.7. Test Specimen7.1 The part to be checked shall be cleaned, using anyacceptable procedure, to remove any foreign material thatmight cause localized optical distortion. No specialconditioning, other than cleaning, is required. The part shall beat ambient temperature.8. Proce
20、dure8.1 The procuring activity shall specify whether Method Aor Method B (see Table 1) or some other set of distances shallbe used to measure optical distortion and deviation. If MethodA or Method B are not used, the actual distances used shall bereported. When the part is flat and mounted nearly ve
21、rtical,MethodAis a more stringent test than Method B. Certain partsmay show substantial optical deviation by Method B simplydue to refraction of the light rays. If the part is a windscreen theprocuring activity may require the camera to be positioned atthe pilots eye position.FIG. 1 Optical Distorti
22、on Represented by TangentTABLE 1 Optical Inspection DistancesMethod ACamera-to-grid-board distance 1000 cm (32 ft 10 in.)Camera-to-part distance 550 cm (18 ft 1 in.)Part-to-grid board distance 450 cm (14 ft 9 in.)Method BCamera-to-grid-board distance 450 cm (14 ft 9 in.)Camera-to-part distance 150 c
23、m (4 ft 11 in.)Part-to-grid-board distance 300 cm (9 ft 10 in.)F733 09 (2014)28.2 Measure optical distortion through the part by thefollowing procedure:8.2.1 Mount the transparent part to be examined firmly toprevent movement during photographing. The mounted angleof the part shall be as specified b
24、y the procuring activity. It isrecommended that the part be mounted at the installed angle.Record the mounted angle, and report with the results.8.2.2 The distances for positioning of camera, part, and gridboard shall be in accordance with Method A or Method B asshown in Table 1 or as determined by
25、the procuring activity. Adepiction of the set up is shown in Fig. 2.8.2.3 Prepare a single exposure photograph of the grid boardviewed through the part. The camera shall be focused on thegrid board.8.3 Photograph optical deviation through the part by thefollowing procedure.8.3.1 Prepare a double exp
26、osure photograph. Photographthe grid board through the part as in 8.2. Then, withoutallowing any movement of the camera, remove the part andmake the second exposure of the grid board alone. If a digitalcamera is used the two exposures can be digitally superim-posed with the aid of a computer and app
27、ropriate software.8.4 Evaluate optical distortion or deviation for the transpar-ent part by projecting or printing the negative suitablyenlarged, and measuring the distortion or deviation. Theprojection or print shall be a minimum of one fifth the lineardimensions of the part photographed. See Fig.
28、1 for onemethod of optical distortion evaluation, and Fig. 3 for anexample of optical deviation. Alternatively, analysis of theimage can be accomplished on a computer (if a digital camerais used) using appropriate image analysis software.9. Calculation9.1 General InformationThe following information
29、 isgiven to aid in the explanation of optical distortion anddeviation measurements:S 5D 31000P(1)where:S = grid square signfiicance in milliradians,D = grid dimension, cm, and,P = part-to-grid-board distance, cm.NOTE 1The camera viewing position line of sight shall be through the center of the pilot
30、s eye position for the part as specified by the procuringactivity.FIG. 2 Example of Installed AngleF733 09 (2014)3M 5CgCp3 G(2)where:M = number of grid lines subtended by the view throughone-linear centimetre of the transparent parts,Cg= camera-to-grid-board distance, cm,Cp= camera-to-part distance,
31、 cm, andG = grid size, cm.9.2 Optical DistortionOptical distortion in a transparentpart can be measured by the following methods:9.2.1 The projected or printed photograph negative or digi-tal image is examined to locate the area of maximum grid linedistortion in either the horizontal or vertical dir
32、ection. Theslope of the distorted grid line is described in terms of gridsquares of run for one grid square of slope. The example shownin Fig. 1 has a slope of one to five.9.2.2 This method expresses optical distortion as milliradi-ans per centimetre of part. The photograph negative or digitalimage
33、is examined as described in 9.2.1 but the angle of slope, (see Fig. 1), is converted to the natural tangent, that is, 0.200.Optical Distortion 5 S 3 M 3Tangent (3)9.2.3 This method of measuring optical distortion is pos-sible when a precision grid is used (all grid squares are ofidentical size 60.15
34、 mm). The distortion is expressed inmilliradians per centimetre of part. The projected or printedphotograph is examined as described in 9.2.1 to locate the areaof maximum distortion. The height, width, or diagonal of themost severely distorted grid square or consecutive squares isaccurately measured
35、 to 63 % of the grid size as projected orprinted. The identical dimension is measured on a true gridsquare or squares (the grid portion outside the area of the part,see Fig. 1). The decimal ratio of the stretch or compression(length change) of the distorted grid section to an identical truegrid sect
36、ion is calculated for example, R = (6.30 mm 5.25mm) 5.25 mm = 0.200.Optical Distortion 5 S 3 M 3 R (4)where:R = decimal ratio of the length change distorted grid sectionto the true grid section.9.3 Optical DeviationIt should be noted that neitherMethod A nor Method B measures the exact optical devia
37、tion(angular deviation, see Test Method F801 for alternativeprocedures) of the part. This is due to refraction of certain ofthe light rays dependent on mounting angle, part contour andthickness, or other factors. This inherent deviation should betaken into account when evaluating the part. Optical d
38、eviationin the part is measured as follows. (Note that this procedureonly works if the part is essentially flat and mounted such thatthe plane of the surface is perpendicular to the optical axis ofthe camera and parallel with the grid board surface.)9.3.1 The projected or printed double exposure pho
39、tographis examined to locate the area of maximum grid line shift ineither the horizontal or vertical direction. Each grid square asphotographed represents a specific angular significance, there-fore the angular deviation, in milliradians is given by:Deviation 5 S 3GT(5)where:S = grid significance in
40、 milliradians,G = maximum grid shift, cm, andT = true grid dimension, cm.See Fig. 3 for an example of optical deviation.10. Precision and Bias10.1 Since this ASTM document is written as a practice, noPrecision and Bias section is required. However, Test MethodsF801 (optical deviation or angluar devi
41、ation) and Test MethodF2156 (optical distortion using grid line slope) address essen-tially the same parameters as this practice does, but, since theyare test methods, they contain Precision and Bias information.11. Keywords11.1 distortion; grid-line slope; optical deviation; opticaldistortion; tran
42、sparency qualityFIG. 3 Optical DeviationDouble ExposureF733 09 (2014)4ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of a
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