1、Designation: F 2469 05Standard Test Method forMeasuring Optical Angular Deviation of Transparent PartsUsing the Double-Exposure Method1This standard is issued under the fixed designation F 2469; the number immediately following the designation indicates the year oforiginal adoption or, in the case o
2、f 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 test method covers the measurement of the opticalangular deviation of a light ray impose
3、d by transparent partssuch as a commercial or military aircraft windshield, canopy orcabin window.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety concerns, if a
4、ny, 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 regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2F 801 Test Method for Measuring Optical Angular D
5、evia-tion of Transparent PartsF 1181 Test Method for Measuring Binocular Disparity inTransparent Parts3. 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 ma
6、terial,which is expressed in units of angle (degree, minutes of arc,milliradians) and is a function of the angle of incidence at eachsurface of the material and the index of refraction of thematerial.3.1.2 design eyethe reference point in aircraft design fromwhich all visual or optical anthropometri
7、cal design consider-ations are taken.3.1.3 grid boardan optical evaluation tool used to detectthe presence of distortion in transparent parts. It is usually, butnot always, a vertical rectangular backboard with horizontaland vertical intersecting lines with maximum contrast betweenthe white lines an
8、d the black background.3.1.4 installed anglethe transparency (windscreen,canopy, or cabin window) orientation as installed in theaircraft, defined by the angle between a horizontal line (line-of-sight) and a plane tangent to the surface of the transparency(see Fig. 1).4. Summary of Test Method4.1 Th
9、e transparent part is mounted, preferably at theinstalled angle, a specified distance from a grid board testpattern. A camera is placed so as to record a double exposurephotograph of the grid pattern as viewed through the transpar-ency from the design eye or other viewing position specified bythe pr
10、ocuring agency. The image is then measured to assess thelevel of optical deviation present. This method basicallymeasures the amount of angular deviation present in a trans-parent part compared to a reference part (if required), which isreferred to as a compensator plate. If the part to be measured
11、isessentially flat and mounted such that its surface is perpendicu-lar to the camera axis then no compensator/reference part isrequired. This is an alternate method to Test Method F 801.5. Significance and Use5.1 The optical angular deviation of transparent parts, suchas aircraft windshields, canopi
12、es, cabin windows, and visors,can be measured using these methods. Angular deviation in awindscreen or visor can cause objects to appear at a locationdifferent from where they actually are. Variations in angulardeviation can be used to characterize distortion and magnifi-cation in transparent parts.
13、 Also, angular deviation measure-ments made from the typical right and left eye positions for awindscreen or other transparent medium can be used todetermine binocular disparity differences (see Test MethodF 1181).6. Apparatus6.1 Test RoomThe test room must be large enough toproperly locate the requ
14、ired testing equipment.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 Mar. 1, 2005. Published March 2005.2For referenced ASTM standards,
15、 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 page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 194
16、28-2959, 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. 2).Grid boards are of the following types:6.2.1 Type 1The
17、 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 providesillumination of
18、 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 each sid
19、e 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 or in
20、candescent 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 t
21、heprocuring 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 spacin
22、g 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 digital camera is acceptable. The camera shall befirmly
23、 mounted at design eye (or position specified by theprocuring agency) to prevent any movement during the pho-tographic exposure.6.4 Compensator PlateThis is a transparent reference thatpossesses the same basic characteristics of the transparencythat will be measured, that is, thickness, shape, index
24、 ofrefraction. If the measurement area is small, a flat plate of glassmay be used. The purpose of the compensator plate is tocompensate for lateral displacement of the reference image ofthe double-exposure images. If the part to be measured isFIG. 1 Example of Installed Angle GeometryF2469052essenti
25、ally flat and it is mounted so that its surface isperpendicular to the optical axis of the camera, then a com-pensator plate may not be required.7. Test Specimen7.1 The transparency to be measured shall be cleaned usingany acceptable procedure, to remove any foreign material thatmight cause localize
26、d optical distortion. No special condition-ing, other than cleaning, is required. The part shall be atambient temperature.8. Procedure8.1 Optical angular deviation in a transparent part can bemeasured by one of the following methods:8.1.1 Photographic Double-Exposure Method:8.1.1.1 Firmly mount the
27、transparent part to be examined toprevent movement during photographing. Mount the part at theinstalled angle, or the angle specified by the procuring agency.Record the mounted angle, and report it with the results.8.1.1.2 Mount the camera at design eye position or otherposition specified by the pro
28、curing agency. Make sure that theoptical axis of the camera is perpendicular to the grid boardsurface and is aimed at the center of the target panel. Forphotographic camera measurement use high resolution blackand white film.8.1.1.3 Place the grid board a specified distance from thecamera as dictate
29、d by the procuring agency (see Fig. 1 forsome suggested distances) and insure that the grid boardpattern is in good focus at the focal plane of the camera.8.1.1.4 Prepare a double-exposure photograph by photo-graphing the grid board through the transparency and then,without allowing any movement of
30、the camera and withoutadvancing the film, remove the part and take the secondexposure of the grid board alone.NOTE 1The second exposure is taken with no transparency in the pathonly if the part is essentially flat and the part is mounted so that its surfaceis essentially perpendicular to the camera
31、axis. If this is not the case, thenthe second exposure must be taken through a reference part and all angulardeviation assessments are made with respect to the angular deviation ofthe reference part. The reference part should have approximately the samethickness, shape, and index of refraction as th
32、e parts to be tested.8.1.1.5 Develop the film and produce 8 by 10 in. mattefinish prints (minimum size). The matte finish will reducereflection problems during measurement.8.1.1.6 Measure optical deviation as follows:8.1.1.7 The double-exposure photograph is examined tolocate the area of maximum gri
33、d line shift in either thehorizontal or vertical direction (see Fig. 3).8.1.1.8 Measure the maximum grid shift from the true gridline in centimeters and calculate deviation according to 9.1.8.1.2 Digital Camera with Template Method:8.1.2.1 Create a template to facilitate angular deviationmeasurement
34、s at specified azimuth and elevation coordinatesin the following manner:8.1.2.2 Firmly mount a laser pointer at the design eyeposition of the transparency that will be measured.8.1.2.3 Cover the compensator plate with tracing paper andmount it at the installed angle of the transparency to bemeasured
35、.8.1.2.4 Rotate the compensator plate in azimuth and eleva-tion around the design eye point to the desired measurementcoordinates.FIG. 2 Grid Board PatternF2469053NOTE 2This procedure assumes a transparency movement table isavailable to move the transparency to the desired azimuth and elevationcoord
36、inates. If such a table is not available the following alternativemethod can be used.(1) Alternatively, the laser pointer can be rotated inazimuth and elevation to point it in the desired measurementazimuth and elevation directions. At each coordinate point tobe measured, draw an outline around the
37、laser beam on thetracing paper. This outline may be on the order of 1 to 2 cm indiameter or may have an elliptical or circular shape dependingon the shape of the transparent part and its orientation. Thepurpose of this is to make a template that will allow easyinterpretation of the double exposure i
38、mage with respect to themeasurement of angular deviation at the desired azimuth andelevation coordinates.8.1.2.5 Remove the tracing paper and cut out the outlinedpoints.8.1.2.6 Transfer the tracing paper to a piece of blackconstruction paper, and trace the outlined measurement pointareas. Cut out th
39、e outlined measurement areas.8.1.2.7 Reposition and attach the black template to thecompensator plate.8.1.2.8 Firmly mount the transparent part to be examined toprevent movement during photographing. Mount the part at theinstalled angle, or the angle specified by the procuring agency.Record the moun
40、ted angle, and report it with the results.8.1.2.9 Mount the digital camera at design eye position orother position specified by the procuring agency. Make surethat the optical axis of the camera is perpendicular to the gridboard surface.8.1.2.10 Place the grid board a specified distance from thecame
41、ra as dictated by the procuring agency and insure that thegrid board pattern is in good focus at the focal plane of thecamera.8.1.2.11 Prepare a double-exposure photograph by photo-graphing the grid board through the transparency and then,without allowing any movement of the camera, remove the parta
42、nd take a photograph through the compensator plate.8.1.2.12 Digitally superimpose the image of the gridthrough the compensator plate (with template) over the imagetaken through the transparency. Print out an 8 by 10 in. mattefinish print (minimum size). The matte finish will reducereflection problem
43、s during measurement.8.1.2.13 Measure optical deviation as follows:8.1.2.14 Locate the center line of each of the measurementareas and measure the maximum grid shift from the true gridline in millimetres and calculate the horizontal and verticalangular deviation according to Section 9. See Fig. 4 fo
44、r anexample of optical deviation using the digital camera andtemplate method.FIG. 3 Example of Double-Exposure Measurement of Optical DeviationF24690549. Calculations9.1 Each grid square as photographed represents a specificangular significance, therefore:Angular deviation 5a5S 3 G/T (1)where:a = an
45、gular deviation in milliradians,S = grid significance in milliradians (the angular subtenseof one grid square),G = grid shift as measured on the photograph, cm, andT = true (undistorted not imaged through the transpar-ency) grid dimension as measured on the photograph,cm.The grid significance, S, is
46、 calculated 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.11.
47、 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 mentionedin this standard. Users of this standard are expressly advised that determination of th
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