1、Designation: E 1951 02 (Reapproved 2007)Standard Guide forCalibrating Reticles and Light Microscope Magnifications1This standard is issued under the fixed designation E 1951; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、 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 guide covers methods for calculating and calibrat-ing microscope magnifications, photographic magnifications
3、,video monitor magnifications, grain size comparison reticles,and other measuring reticles. Reflected light microscopes areused to characterize material microstructures. Many materialsengineering decisions may be based on qualitative and quan-titative analyses of a microstructure. It is essential th
4、at micro-scope magnifications and reticle dimensions be accurate.1.2 The calibration using these methods is only as precise asthe measuring devices used. It is recommended that the stagemicrometer or scale used in the calibration should be traceableto the National Institute of Standards and Technolo
5、gy (NIST)or a similar organization.1.3 This standard does not purport to address all of thesafety concerns, if any, 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 limit
6、ations prior to use.2. Referenced Documents2.1 ASTM Standards:2E7 Terminology Relating to MetallographyE112 Test Methods for Determining Average Grain Size3. Terminology3.1 DefinitionsAll terms used in this guide are defined inTerminology E7.4. Significance and Use4.1 These methods can be used to de
7、termine magnificationsas viewed through the eyepieces of light microscopes.4.2 These methods can be used to calibrate microscopemagnifications for photography, video systems, and projectionstations.4.3 Reticles may be calibrated as independent articles and ascomponents of a microscope system.5. Proc
8、edures5.1 Nominal Magnification Calculations:5.1.1 A calculated magnification, using the manufacturerssupplied ratings, is only an approximation of the true magni-fication, since individual optical components may vary fromtheir marked magnification. For a precise determination of themagnification ob
9、served through an eyepiece, see the proceduredescribe in 5.5.5.1.2 For a compound microscope, the total magnification(Mt) of an image through the eyepiece is the product of theobjective lens magnification (Mo), the eyepiece magnification(Me), and, if present, a zoom system or other intermediate lens
10、magnification (Mi). An expression for the total magnification isshown in Eq 1.Mt5 Mo3 Me3 Mi(1)5.1.3 Example 1For a microscope configured with a 10Xobjective, a 10X eyepiece, and a 1.25X intermediate lens, thetotal magnification observed through the eyepiece would becalculated as follows.Mt5 10!10!1
11、.25! 5 125 (2)5.2 Calibration for Photomicrography Magnifications:5.2.1 The magnification of an image can be determined byphotographing a calibrated stage micrometer using the desiredoptical setup. First, photograph the stage micrometer using thedesired combination of objective, bellows extension, z
12、oom andintermediate lens, and then measure the apparent ruling lengthon the photomicrograph. The measurement should be madeconsistently from an edge or center of one division to thecorresponding edge or center of another (see Note 1). Bydividing this apparent length of ruling by the known dimensiono
13、f the micrometer, the magnification of the photomicrograph isdetermined (see Fig. 1). The accuracy of the calibration isdependent on the accuracy of the calibrated stage micrometerand the scale used to measure the apparent length of thephotographed ruling.1This guide is under the jurisdiction of AST
14、M Committee E04 onMetallographyand is the direct responsibility of Subcommittee E04.03 on Light Microscopy.Current edition approved Oct. 1, 2007. PublishedOctober 2007.Originally approved in 1998. Last previous edition approved in 2002 asE 195102.2For referenced ASTM standards, visit the ASTM websit
15、e, 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 19428-2959, United States
16、.NOTE 1The choice of using the edge or center of a reticle linedepends on the method of manufacture used to produce the measuringdevice. Some devices are calibrated from center to center while others aremeasured from one edge to another. Consult with the manufacturer todetermine which method should
17、be employed.5.2.2 Example 2For a metallograph with a given configu-ration (50X objective), determine the calibrated magnificationof a photomicrograph.5.2.2.1 A photograph of a stage micrometer was taken (Fig.1). A rule was overlaid. From one corresponding edge of adivision to another, using the rule
18、, a distance of 62 mm wasmeasured over a known distance of 0.12 mm on the photographof the stage micrometer. Dividing 62 mm by 0.12 mm yields aphotographic magnification of 517X.5.2.3 By photographing a stage micrometer using variouscombinations of objectives, intermediate lenses, zoom andbellows ex
19、tensions, a table can be produced which summarizesthe possible magnifications of a system.3Microscopes incor-porating devices allowing continuous magnification ranges(zooms) should not be used for critical measurements, exceptby including reference photos of traceable reticles takenconcurrently with
20、 the measured item. Mechanical play in thesedevices can be a significant source of error.5.3 Calibration for Projection Screens, Video Systems, andVideo Printers:5.3.1 For projection screens that are not also photographicstations and for video monitors, the magnification can becalibrated as follows.
21、 Focus an image of a stage micrometer onthe screen, and then measure the projected apparent length ofthe ruling. If convenient, the measurement can be madedirectly on the screen, or by transferring the apparent length toa scale using pinpoint dividers. It should not be assumed that avideo system has
22、 the same magnification in the x (horizontal)and y (vertical) axis. Further, it should not be assumed that theratio of the magnification in the x direction versus the ydirection is equal to the ratio of the dimensions of an individualpixel in the x and y directions. The measurement should bemade con
23、sistently from an edge or center of one division to thecorresponding edge or center of another. The magnification iscalculated by dividing the measured apparent length by theknown dimensions of the micrometer (see Example 2 in 5.2.2and Fig. 1).5.3.2 Magnifications of video prints should be calibrate
24、d byuse of a print or prints of two measuring devices, one placed oneach axis of a single print or one placed on opposite axes ontwo separate prints. This calibration print should be producedat the same magnification as the prints of interest. Exercise careto ensure that the aspect ratio of the obje
25、ct is reproducedaccurately in the print, as the x and y dimensions of the finalprint can be adjusted independently through the controlsprovided on some printers.5.3.3 Most high quality video printers will allow someadjustment of the final print dimensions. Major adjustments tomagnification should be
26、 made by use of intermediate projec-tion lenses or microscope objectives. Increasing magnificationby use of video printer controls is not recommended due to thedegradation of resolution.5.4 Eyepiece Micrometer Calibration:5.4.1 To calibrate an eyepiece micrometer reticle, viewthrough the eyepiece an
27、 image of a stage micrometer using agiven objective and intermediate lens combination. Overlay theeyepiece micrometer image on the stage micrometer image,with one end of each coincident upon one another. Themeasurement should be made consistently from an edge of onedivision to the corresponding edge
28、 of another (Fig. 2). Theeyepiece reticle calibration can be determined by dividing theknown length of the stage micrometer by the number of3Vander Voort, G. F., Metallography, Principles and Practice, McGraw Hill, NewYork, NY, 1984, pp. 279-280.NOTE 1This schematic shows the procedure used to deter
29、mine the calibrated magnifications of video screens, video printers, projection screens, andphotographs.FIG. 1 Procedure for Determining Calibrated MagnificationsE 1951 02 (2007)2overlaid eyepiece micrometer divisions. This calculation yieldsa length per division value of the micrometer for a giveno
30、ptical setup.5.4.2 Example 3For a given microscope configuration(40X objective), determine the length per division value of aneyepiece micrometer.5.4.2.1 The image of the eyepiece micrometer was alignedwith the stage micrometer image (Fig. 2). Eighty-five divisionswere counted over a distance of 0.2
31、1 mm on the stagemicrometer. The length per division can then be calculated asfollows.0.21 mm / 85 divisions! 1000 m/1mm! 5 2.4752.5 m/division(3)5.4.3 Repeat the procedure listed above for various objec-tive and intermediate lens combinations to create a table ofeyepiece micrometer calibrations.NOT
32、E 2In order for the magnification to be consistent from user touser, the eyepiece reticle must be focussed for the users eyes beforefocusing the microscope on the image as produced by the objective. Also,the positioning of the reticle in the eyepiece must be repeatable.NOTE 3Caution must be observed
33、 if both eyepiece tubes are adjust-able. Also, change in interpupillary distance may change the magnifica-tion, particularly in older microscopes.5.5 Magnification Calibration of Image Viewed ThroughEyepieces:5.5.1 This procedure will give a calibrated magnificationobserved through the eyepieces of
34、a particular microscope lensconfiguration, independent of the user (Fig. 3).5.5.2 Focus the image of a stage micrometer through theeyepieces. This procedure will require a stage micrometer withhigh contrast markings.5.5.3 Determine the position of the eyepoint of the systemas follows: (1) adjust the
35、 lighting on the microscope to amaximum, (2) place an opaque or translucent piece of materialperpendicular to the light path.Acircular projection of the lightNOTE 1This schematic diagram illustrates the procedure used to calibrate an eyepiece measuring reticle.FIG. 2 Diagram for Calibrating an Eyepi
36、ece Measuring ReticleE 1951 02 (2007)3will appear. (3) Move the material away from the eyepiece lensuntil the size of the circular light beam becomes a minimum.Initially, the size of the beam will decrease until the eyepointdistance is reached, then at a distance greater than the opticaleyepoint, th
37、e size of the circular projection will increase. (4)Note the distance of the eyepoint from the eyepiece lens.5.5.4 Place an unexposed piece of film or a rigid piece ofviewing medium, such as ground glass, perpendicular to thelight path at a point 250 mm plus the eyepoint distance awayfrom the eyepie
38、ce lens. The calibration measurement can thenbe made directly on the ground glass or on the developed filmor resulting print. The calibration is completed by placing thedivisions of a rule coincident upon the projected image of thestage micrometer. The alignment should be made consistentlyfrom an ed
39、ge of one division to the corresponding edge ofanother. (A large-format bellows camera, without lens, may beconveniently used here. If this is done, a film of the image canalso be exposed, with the calibration then performed on thedeveloped film.)5.5.5 Determine the observed magnification by dividin
40、g themeasured length of the projected section of the stage microme-ter by the known length of that section of the stage micrometer.5.5.6 Repeat this procedure for various objective and inter-mediate lens combinations to create a table of observablemagnifications.5.5.7 Example 4Determine the magnific
41、ation viewedthrough an eyepiece with a microscope configuration consist-ing of a 10X objective and a 10X eyepiece.5.5.7.1 Using an overhead transparency, and a rule placedperpendicular to the plane of the eyepiece lens, the eyepointwas determined to be at a distance of 18 mm. Next, a distanceof 268
42、mm was measured perpendicular from the plane of theeyepiece.5.5.7.2 Aviewing medium was fixed at this distance parallelto the plane of the eyepiece lens. The divisions of a rule wereplaced coincident upon the projected image of the stagemicrometer consistently from an edge of one division to thecorr
43、esponding edge of another. A distance of 89 mm wasmeasured over a known distance of 0.9 mm on the stagemicrometer. By dividing the measured length by the knownlength a calibrated magnification of 99X was determined.5.6 Filar Eyepiece Calibration:5.6.1 The calibration of a filar measuring eyepiece is
44、 similarto that of an eyepiece reticle as illustrated in Fig. 2. Themoveable cross-hair in the eyepiece is positioned at an extremeNOTE 1A schematic diagram illustrating the procedure used to determine the magnification observed through the microscope eyepieces.FIG. 3 Diagram for Magnification Obser
45、ved Through Microscope EyepiecesE 1951 02 (2007)4end of a stage micrometer coincident with one micrometerdivision. The measurement should be made consistently froman edge or the center of one division to another.5.6.2 For a drum filar eyepiece, note the micrometer drumvalue. Traverse the cross-hair
46、over as many micrometer divi-sions as possible that are visible in the central region of thefield of view. Note the new micrometer drum value. To obtainthe total drum movement, subtract the final drum value fromthe initial value. The value of each increment on the filar drumis determined by dividing
47、 the actual length traversed on thestage micrometer by the total drum movement. Repeat thisprocedure for each objective of interest. This calculation issimilar to that of determining an eyepiece micrometer calibra-tion ( Example 3 in Section 5.4.2.1).5.6.3 For digital filar eyepieces, a multiplier m
48、ust by deter-mined for each objective.5.6.3.1 To determine the value of the multiplier for aspecific microscope configuration, set the multiplier to one, andtraverse a known distance.5.6.3.2 The value of the multiplier is determined by dividingthe known distance traversed by the value determined by
49、thefilar eyepiece.5.6.3.3 Next, set the instrument to zero, and enter theapproximate multiplier into the system. Traverse the stagemicrometer as described in the previous section. If the mea-sured distance is incorrect, adjust the multiplier accordingly.Reset to zero, and traverse the stage micrometer again.5.6.3.4 Repeat these steps until an accurate multiplier hasbeen determined for each objective.5.6.3.5 Example 5Determine the digital filar eyepiecemultiplier for a given microscope configuration. (50X objec-tive).After setting the multiplier to 1, a distanc
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