1、Designation: F 733 90 (Reapproved 2003)Standard 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
2、the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 li
3、ne 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 This standard does not purport to address the safetyconcerns associated with
4、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. Terminology2.1 Definitions:2.1.1 deviationthe displacement of a line or object whenviewed through the transpare
5、nt part. Expressed as the angularmeasurement of the displaced line, for example, milliradians ofangle.2.1.2 distortionthe rate of change of deviation resultingfrom an irregularity in a transparent part.2.1.3 Expressed as the angular bending of the light ray perunit of length of the part, for example
6、, milliradians percentimetre.2.1.4 May also be expressed as the slope of the angle oflocalized grid line bending, for example, 1 in 5 (see Fig. 1).2.1.5 installed anglethe part attitude as installed in theaircraft. Defined by the angle from a horizontal line to thevertical plane of the part, and the
7、 angle of sweep back from ahorizontal line normal to the center line of the aircraft. See Fig.2 for an example.3. Summary of Practice3.1 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 pho
8、tograph is thenexamined and optical distortion or deviation is measured.4. Significance and Use4.1 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 acc
9、eptability against thespecification for the part. The photograph (print or negative)can be maintained as a permanent record of the optical qualityof the part.5. Apparatus5.1 Test RoomThe test room must be large enough toproperly locate the required testing equipment.5.1.1 Method A requires a room ap
10、proximately 12 m (40 ft)long.5.1.2 Method B requires a room approximately 7 m (23 ft)long.5.1.3 The walls, ceiling, and floor shall have low reflec-tance. A flat black paint or coating is preferred.5.2 Grid BoardThe grid board provides a defined patternagainst which the transparent part is examined.
11、 Grid boards areof the following types.5.2.1 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 f
12、luorescent lights at each side providesillumination of the strings.5.2.2 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 pat
13、tern withexcellent photographic characteristics.5.2.3 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.5.2.4 The grid board shall have a width and hei
14、ght 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 (12 in.), or more than 2.54 cm (1 in.).1T
15、his 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 Oct. 1, 2003. Published November 2003. Originallyapproved in 1981. Last previous edition appro
16、ved in 1997 as F 733 90 (1997)e1.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.3 CameraUnless otherwise specified, the camera shallutilizea4by5-in. film size. The lens opening used shall be f 8or smaller. The camera shall be firm
17、ly mounted to prevent anymovement during the photographic exposure.6. Test Specimen6.1 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
18、part shall be atambient temperature.7. Procedure7.1 The procuring activity shall specify whether Method Aor Method B (see Table 1) shall be used to measure opticaldistortion and deviation. When the part is flat and mountednearly vertical, Method A is a more stringent test than MethodB. Certain parts
19、 may show substantial optical deviation byMethod B simply due to refraction of the light rays.7.2 Measure optical distortion through the part by thefollowing procedure:7.2.1 Mount the transparent part to be examined firmly toprevent movement during photographing. The mounted angleof the part shall b
20、e as specified by the procuring activity. It isrecommended that the part be mounted at the installed angle.Record the mounted angle, and report with the results.7.2.2 The distances for positioning of camera, part, and gridboard shall be in accordance with Method A or Method B asshown in Table 1. A d
21、epiction of the set up is shown in Fig. 2.7.2.3 Prepare a single exposure photograph of the grid boardviewed through the part. The camera shall focus on the gridboard.7.3 Photograph optical deviation through the part by thefollowing procedure.7.3.1 Prepare a double exposure photograph. Photographthe
22、 grid board through the part as in 7.2. Then, withoutallowing any movement of the camera, remove the part andmake the second exposure of the grid board alone.7.4 Evaluate optical distortion or deviation for the transpar-ent part by projecting or printing the negative suitably en-larged, and measurin
23、g the distortion or deviation. The projec-tion or print shall be a minimum of one fifth the linearFIG. 1 Optical Distortion Represented by TangentTABLE 1 Optical Inspection DistancesMethod ACamera-to-grid-board dis-tance1000 cm (32 ft 10 in.)Camera-to-part distance 550 cm (18 ft 1 in.)Part-to-grid b
24、oard distance 450 cm (14 ft 9 in.)Method BCamera-to-grid-board dis-tance450 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.)F 733 90 (2003)2dimensions of the part photographed. See Fig. 1 for onemethod of optical distortion evaluation, and
25、Fig. 3 for anexample of optical deviation.8. Calculation8.1 General InformationThe following information isgiven to aid in the explanation 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-bo
26、ard distance, cm.M 5CgCp3 G(2)NOTE 1The camera viewing position line of sight shall be through the center of the pilots eye position for the part as specified by the procuringactivity.FIG. 2 Example of Installed AngleFIG. 3 Optical DeviationDouble ExposureF 733 90 (2003)3where:M = number of grid lin
27、es 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.8.2 Optical DistortionOptical distortion in a transparentpart can be measured by the following methods:8.2.1 The projected or pri
28、nted photograph negative is ex-amined to locate the area of maximum grid line distortion ineither the horizontal or vertical direction. The slope of thedistorted grid line is described in terms of grid squares of runfor one grid square of slope. The example shown in Fig. 1 hasa slope of one to five.
29、8.2.2 This method expresses optical distortion as milliradi-ans per centimetre of part. The photograph negative is exam-ined as described in 8.2.1 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)8.2.3 This method of
30、 measuring optical distortion is pos-sible when a precision grid is used (all grid squares are ofidentical size 60.15 mm). The distortion is expressed inmilliradians per centimetre of part. The projected or printedphotograph is examined as described in 8.2.1 to locate the areaof maximum distortion.
31、The height, width, or diagonal of themost severely distorted grid square or consecutive squares isaccurately measured 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 d
32、ecimal ratio of the stretch or compression(length change) of the distorted grid section to an identical truegrid section is calculated that is, R = (6.30 mm 5.25 mm) 45.25 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
33、 section.8.3 Optical DeviationIt should be noted that neitherMethod A nor Method B measures the exact optical deviationof the part. This is due to refraction of certain of the light raysdependent on mounting angle, part contour and thickness, orother factors. This inherent deviation should be taken
34、intoaccount when evaluating the part. Optical deviation in the partis measured as follows.8.3.1 The projected or printed double exposure photographis examined to locate the area of maximum grid line shift ineither the horizontal or vertical direction. Each grid square asphotographed represents a spe
35、cific angular significance, there-fore:Deviation 5 S 3GT(5)where:S = grid significance in milliradians,G = maximum grid shift, cm, andT = true grid dimension, cm.See Fig. 3 for an example of optical deviation.9. Precision and Bias9.1 It is not practicable or justifiable to specify the precisionand b
36、ias of the procedure in this practice for measuring opticaldistortion and deviation because of the operator-sensitivenature in the measurement of the test photos.10. Keywords10.1 distortion; grid-line slope; optical deviation; opticaldistortion; transparency qualityASTM International takes no positi
37、on 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 riskof infringement of such rights, are entirely their own responsibility
38、.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 this standard or for additional standardsand should be addressed to ASTM
39、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 shouldmake your views known to the ASTM Committee on Standards, at the address sh
40、own 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).F 733 90 (2003)4
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