1、Designation: F801 96 (Reapproved 2008)F801 16Standard Test Method forMeasuring Optical Angular Deviation of Transparent Parts1This standard is issued under the fixed designation F801; the number immediately following the designation indicates the year of originaladoption or, in the case of revision,
2、 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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This test method covers
3、 measuring the angular deviation of a light ray imposed by transparent parts such as aircraftwindscreens and canopies. The results are uncontaminated by the effects of lateral displacement, and the procedure may beperformed it is possible to perform the procedure in a relatively short optical path l
4、ength. This is not intended as a referee standard.It is one convenient method for measuring angular deviations through transparent windows.1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard t
5、o establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodF2156 Test Method for Measuring Optica
6、l Distortion in Transparent Parts Using Grid Line SlopeF733 Practice for Optical Distortion and Deviation of Transparent Parts Using the Double-Exposure Method3. Terminology3.1 Definitions:3.1.1 angular deviationthe departure of a light ray from its original path as it passes through a transparent m
7、aterial. Thechange in angle of such a light ray. The displacement of an image due to the change in direction of the light ray.3.1.2 lateral (or linear) displacementthe shift or movement of a light ray from its original path as it passes through atransparent material, while maintaining parallelism be
8、tween the original and final paths. The change in location of an image dueto this change in path.3.1.3 modulation transfer function (MTF)the ratio of output modulation to the input modulation. The modulus of the Fouriertransform of the optical spread function.4. Summary of Test Method4.1 This test m
9、ethod outlines how measurements can be provides a basic procedure for measuring the angular deviation inducedby a transparent part. Angular deviation measurements are made by an optoelectronic system employing collimated light, lightfrom an appropriate target pattern, a field lens, and a position-de
10、tecting device/system such as linear diode arrays as the part is heldor a two-dimensional diode array. Hold the transparent part either in its installed angle. The positions of two images of a angleor perpendicular to the collimated light source are recorded using two linear diode arrays. One array
11、records azimuth or horizontalposition while the other records elevation or vertical position. These arrays are at the posterior focal plane of a field lens. Thepositions are again recorded after the interposition of a transparent part in the optical path. The difference in image position isdirectly
12、related toor any other orientation suitable for the purpose of making the measurement. One specific optoelectronic systemsuitable for conducting this test method is provided in Appendix X2 and Appendix X3 the angular deviation imposed by the1 This test method is under the jurisdiction of ASTM Commit
13、tee F07 on Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on TransparentEnclosures and Materials.Current edition approved April 1, 2008April 1, 2016. Published April 2008April 2016. Originally approved in 1983. Last previous edition approved in 20022008 asF801 96 (200
14、2).(2008). DOI: 10.1520/F0801-96R08.10.1520/F0801-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This doc
15、ument is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as
16、 appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1transparent part. The effects of lateral displacement ar
17、e removed by the field lens. Sensitivity of measurement may be controlledby choosing appropriate focal length field lenses and spacing of elementsand in Section 6 on the diode arrays.below.5. Significance and Use5.1 One of the measures of optical quality of a transparent part is its angular deviatio
18、n. Excessive It is possible that excessiveangular deviation, or variations in angular deviation throughout the part, will result in visible distortion of scenes viewed throughthe part. Angular deviation, its detection, and quantification are of extreme importance in the area of certain aircraft tran
19、sparencyapplications, that is, aircraft equipped with Heads-up Displays (HUD). HUDs mayIt is possible that HUDs will require stringentcontrol over the optics of the portion of the transparency (windscreen or canopy) which lies between the HUD combining glassand the external environment. Military air
20、craft equipped with HUDs or similar devices require precise knowledge of the effectsof the windscreen or canopy on image position in order to maintain weapons aiming accuracy.5.2 Two optical parameters have the effect of changing image position. The first, lateral displacement, is inherent in anytra
21、nsparency which is tilted with respect to the line of sight.The effect of lateral displacement is constant over distance, and seldomexceeds a fraction of an inch. The second parameter, angular deviation, is usually caused by a wedginess or nonparallelism of thetransparency surfaces. The effect of an
22、gular deviation is related to the tangent of the angle of deviation, thus the magnitude of theimage position displacement increases as does the distance between image and transparency. The quantification of angulardeviation is then the more critical of the two parameters.6. Apparatus6.1 Transmitter,
23、 capable of projecting collimated light rays from a suitable target. The target may is allowed to be a transparentcrosssmall hole, a transparent cross, or an “L” with one arm horizontal and one arm vertical, embedded in an opaque background.The stroke width of the “L” or cross shall be uniform. Choi
24、ce of an “L” or a cross is optional, since only one half of the crosstarget is used at any time. The transmitter shouldshall be firmly affixed to the floor or other stationary fixture. Note that the choiceof the transmitter target shall be compatible with the position detecting mechanism in the rece
25、iver.6.2 Receiver, shall be firmly affixed to the floor or a stable platform, consisting of the following components:6.2.1 Displacement Compensation and Imaging LensThe sensitivity of the instrument is in part determined by the focal lengthof the lens. An appropriate focal length may be is likely to
26、 be (but is not limited to) 10 in. (254 mm).6.2.2 Optical Beam Splitter, to separate the incoming light into two orthogonal elements; one for elevation and the other forazimuth. The type of beam splitter shouldshall be chosen to keep both optical path lengths equal.6.2.3 Two Linear Charge Coupled De
27、vices (CCD or diode) Arrays, each located at the focal plane of the displacementcompensating lens. One array is oriented horizontally (for the measurement of azimuthal changes), and the other oriented vertically(for the measurement of elevation changes). An appropriateA convenient element spacing of
28、 the arrays is 0.001 in. (0.0254 mm).Using this element spacing, and the 10-in. (254-mm) lens, each diode will represent represents the equivalent of 0.1 milliradian(mrad) angular deviation.6.2.4 Electronic System that will determinecapable of determining the center diode of the band of illuminated
29、diodes on eachCCD array.6.2.5 Electronics System that will convert the number to capable of converting the diode number to an angular deviation to bedisplayed on a digital readout.6.3 Transmitter and Receiver Lenses should are permitted to be of achromatic construction to reduce the effect of aberra
30、tionson the measurement.6.4 Dioptometer, to verify attainment of collimated light.6.5 For further information on the rationale and development of the design see the appendixes. (Appendix X1 Appendix X4.)7. Test Specimen7.1 The part to be tested shouldshall be positioned in such a manner as to approx
31、imate its installed configuration. configurationor positioned as specified by the agency requesting the test. No special conditioning other than cleaning is required.8. Calibration and Standardization8.1 Position the transmitter and receiver so that the optical axes of both are parallel and approxim
32、ately colinear. The light fromthe transmitter shall pass through the test specimen to fall on the receiver lens. Depending on the configuration of the test specimen,locate the transmitter and receiver approximately 4 ft (305(1219 mm or less) apart.This distance depends on the specific equipmentused
33、and is not critical (see Appendix X4 for more information).8.2 Adjust If necessary, adjust the transmitter lens or target position to provide collimated light. A dioptometer is sufficient forthis adjustment.8.3 Adjust If necessary, adjust the receiver field lens and positions of the CCD arrays so ea
34、ch array is at the focal plane of thereceiver lens. Perform rough adjustment by using the receiver lens to sharply focus the target from the previously adjustedF801 162transmitter. Check by interposing a thick optical flat (plane parallel-sided transparent plate) in the optical path, and tilting the
35、 flatwith respect to the optical axis. When correctly adjusted, there will be no movement of the transmitter image at the plane of theCCD array. If the image moves (the readout varies by more than 0.1 mrad), adjust the position of the appropriate CCD array toeliminate this movement.8.4 An A method o
36、f conducting an accuracy test may be is made by interposing a standard or highly accurate optical wedgein the light path between transmitter and receiver. The display shouldshall accurately indicate the angular deviation imposed bythe optical wedge in both the vertical or horizontal meridians. An al
37、ternative method would be to tilt the transmitter or receiveron an accurate tilt table.The tilt, converted to milliradians, shouldshall equal that shown on the display.The latter method is usuallypreferable since it yields a continuous accuracy check over the entire range of measurement.8.5 Amethod
38、of performing a check to ensure operation of all diodes may be is performed by illuminating the entire CCD arrayand noting the default reading on the display. (This default reading is also dependent on the specific circuitry used, but should beisideally a constant).NOTE 1The area of transparency bei
39、ng measured at any one time is related to the smallest diameter lens being used at the transmitter or receiver.The system will average angular deviations throughout a subset of this area. Use of lenses of significantly larger or smaller diameters will affectrepeatability of measurement from one inst
40、rument to another. Use of lenses with small diameters will improve performance on transparencies with rapidlychanging angular deviations, but will reduce available light energy at the CCD array, possibly below its threshold. Lens size is further discussed in theannex.Appendixes.8.6 Certain variation
41、s mayIt is possible that certain variations will be as a result of the following sources of error:8.6.1 Transmitter or receiver lens malfocus. Noncollimated light from the transmitter will cause the receiver to measure somelateral displacement as well as angular deviation.8.6.2 Poor transparency opt
42、ics (MTF or modulation transfer function losses) will cause a blurred image on CCD arrays. If thisblur is asymmetric, it is possible that some error will be introduced. If the MTF loss is great enough, it is possible that the lightenergy will fall below the threshold of the CCD array, and a no-readi
43、ng condition will result.9. Procedure9.1 Mount the transparent part on a fixture that allows accurate determination of the elevation and azimuth position of the part.9.2 Locate and firmly mount the transmitter at an appropriate position corresponding to the observational point of interest(pilots (fo
44、r example: pilots eye designed position), or along a line connecting this point with the receiver lens.9.3 Locate and firmly mount the receiver external to the transparent part and at a distance of 4.9 ft (1.5 m) from thetransmitter.suitable distance from the transmitter (see Appendix X4).9.4 Establ
45、ish a baseline or zero determination without a transparency in the optical path. Record the number as displayed onthe digital readout under this condition.condition (depending on the electronic system used, this value will be zero or adjustableto zero).9.5 Locate the transparency between the transmi
46、tter and receiver. Take readings at points specified by the using activity byrotating the canopy about a critical point such as the pilots eye position or other position of interest specified by the using activity.The difference between these readings and the baseline figures solely represent the an
47、gular deviation in milliradians through eachpoint.10. Calculation10.1 With appropriate selection of receiver lens focal length and CCD array diode separation, the display readout will be in0.1-mrad increments. The 0.1-milliradian increments. It is possible to vary the sensitivity of the instrument m
48、ay be varied byaltering either of these parameters. Assuming a 0.001 in. (0.025 mm) diode spacing as standard, increasing the focal length willimprove the sensitivity as follows:a 5arc tan0.001/f!where:a = sensitivity (minimum measurable angle), mrad andf = focal length of receiver lens, in.10.2 Alt
49、hough the separation distance between the projector and receiver is not critical and does not affect the measurementaccuracy, it does have an effect on both the light energy at the image plane and the maximum amounts of angular deviation thatcan be measured. The Calculate the largest distance from the optical axis at the image plane that does not produce vignetting maybe calculated as follows:H 5f23d22d1!/2Swhere:H = maximum unvignetted ray height at image plane,F801 163d2 = diameter of receiver lens,d1 = diameter of transmitter lens,S = separation between transmitte
