1、Designation: F 733 09Standard Practice forOptical Distortion and Deviation of Transparent Parts Usingthe Double-Exposure Method1This standard is issued under the fixed designation F 733; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisi
2、on, 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 photographic practice determines the optical dis-tortion and deviation of a line of sight through
3、 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 F 801 addresses optical deviation (angluardeviation) and Test Method F 2156 addresse
4、s optical distortionusing grid line slope. These test methods should be usedinstead of Practice F 733 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
5、healthpractices and determine the applicability of regulatory limita-tions prior to use.2. Referenced Documents2.1 ASTM Standards:F 801 Test Method for Measuring Optical Angular Devia-tion of Transparent PartsF 2156 Test Method for Measuring Optical Distortion inTransparent Parts Using Grid Line Slo
6、pe3. 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
7、 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 attitud
8、e 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
9、 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 pr
10、actice, 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 T
11、est 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 o
12、r 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 vertical
13、ly 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.6.2.2 Type 2The grid board is a transparent sheet havingan opaque, flat black outer surface except for the g
14、rid lines. Thegrid lines are left transparent, and when lighted from behind1This 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 May 15, 2009. Pub
15、lished June 2009. Originallyapproved in 1981. Last previous edition approved in 2003 as F 733 90 (2003).1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.with fluorescent lights, provide a bright grid pattern withexcellent photographic
16、 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 are
17、a 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 CameraUnless otherwise specif
18、ied, 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 size of part to be measured
19、.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 special condition-ing, other than cleaning, is required. The part shall be atambient temperature.8. Procedure8.1 The procuring
20、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 vertical,MethodAis a mor
21、e 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.8.2 Measure optical distortion through the pa
22、rt by thefollowing procedure:8.2.1 Mount the transparent part to be examined firmly toprevent movement during photographing. The mounted angleFIG. 1 Optical Distortion Represented by TangentTABLE 1 Optical Inspection DistancesMethod ACamera-to-grid-board distance 1000 cm (32 ft 10 in.)Camera-to-part
23、 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 cm (4 ft 11 in.)Part-to-grid-board distance 300 cm (9 ft 10 in.)F733092of the part shall be as specified by the procuring activity. It i
24、srecommended 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 the procuring activity. Adepic
25、tion 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 exposure photograph. Photographth
26、e 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 appropriate software.8.4 Evaluate
27、 optical distortion or deviation for the transpar-ent part by projecting or printing the negative suitably en-larged, and measuring the distortion or deviation. The projec-tion or print shall be a minimum of one fifth the lineardimensions of the part photographed. See Fig. 1 for onemethod of optical
28、 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 isgiven to aid in the exp
29、lanation of optical distortion anddeviation measurements:S 5D 3 1000P(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 pilots eye position for the pa
30、rt as specified by the procuringactivity.FIG. 2 Example of Installed AngleF733093M 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, cm, andG = grid size, cm.9.2 Opt
31、ical 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 direction. Theslope of the distorted
32、 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 is examined as described in 9.2.1
33、 but the angle of slope,u (see Fig. 1), is converted to the natural tangent, that is, 0.200.Optical Distortion 5 S 3 M 3 Tangent u (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 mm). The distortion is expre
34、ssed 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 to 63 % of the grid size as
35、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 section is calculated for example
36、, R = (6.30 mm 5.25mm) 4 5.25 mm = 0.200.Optical Distortion 5 S 3 M 3 R (4)where:R = decimal ratio of the length change distorted gridsection to the true grid section.9.3 Optical DeviationIt should be noted that neitherMethod A nor Method B measures the exact optical deviation(angular deviation, see
37、 Test Method F 801 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 deviationin the part is mea
38、sured 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 photographis examined to loca
39、te 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 milliradians,G = maximum
40、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 MethodsF 801 (optical deviation or angluar deviation) and Test MethodF 2
41、156 (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; transparency qualityFIG. 3 O
42、ptical DeviationDouble ExposureF733094ASTM 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 any such patent rights, and the r
43、iskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of t
44、his standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmak
45、e 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 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).F733095
