1、Designation: E1951 02 (Reapproved 2007)E1951 14Standard Guide forCalibrating Reticles and Light Microscope Magnifications1This standard is issued under the fixed designation E1951; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e 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 guide covers methods for calculating and calibrating microscope magnifications, photographic magnificat
3、ions, videomonitor magnifications, grain size comparison reticles, and other measuring reticles. Reflected light microscopes are used tocharacterize material microstructures. Many materials engineering decisions may be based on qualitative and quantitative analysesof a microstructure. It is essentia
4、l that microscope magnifications and reticle dimensions be accurate.1.2 The calibration using these methods is only as precise as the measuring devices used. It is recommended that the stagemicrometer or scale used in the calibration should be traceable to the National Institute of Standards and Tec
5、hnology (NIST) ora similar organization.1.3 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 to establish appropriate safety and health practices and determine the applicability of regulatoryli
6、mitations 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 in Terminology E7.4. Significance and Use4.1 These methods can be used t
7、o determine magnifications as viewed through the eyepieces of light microscopes.4.2 These methods can be used to calibrate microscope magnifications for photography, video systems, and projection stations.4.3 Reticles may be calibrated as independent articles and as components of a microscope system
8、.5. Procedures5.1 Nominal Magnification Calculations:5.1.1 Acalculated magnification, using the manufacturers supplied ratings, is only an approximation of the true magnification,since individual optical components may vary from their marked magnification. For a precise determination of the magnific
9、ationobserved through an eyepiece, see the procedure describe in 5.5.5.1.2 For a compound microscope, the total magnification (Mt) of an image through the eyepiece is the product of the objectivelens magnification (Mo), the eyepiece magnification (Me), and, if present, a zoom system or other interme
10、diate lens magnification(Mi). An expression for the total magnification is shown in Eq 1.Mt 5Mo 3Me 3Mi (1)5.1.3 Example 1For a microscope configured with a 10X objective, a 10X eyepiece, and a 1.25X intermediate lens, the totalmagnification observed through the eyepiece would be calculated as follo
11、ws.1 This guide is under the jurisdiction of ASTM Committee E04 on Metallography and is the direct responsibility of Subcommittee E04.03 on Light Microscopy.Current edition approved Oct. 1, 2007. Published October 2007.Current edition approved Nov. 1, 2014. Published December 2014. Originally approv
12、ed in 1998. Last previous edition approved in 20022007 asE1951E195102(2007).02. DOI: 10.1520/E1951-02R07.10.1520/E1951-14.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refe
13、r to the standards Document Summary page on the ASTM website.This document 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 cha
14、nges accurately, ASTM recommends that users consult prior editions as 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. U
15、nited States1Mt 510!101.25!5125 (2)Mt 51031031.255125 (2)5.2 Calibration for Photomicrography Magnifications:5.2.1 The magnification of an image can be determined by photographing a calibrated stage micrometer using the desired opticalsetup. First, photograph the stage micrometer using the desired c
16、ombination of objective, bellows extension, zoom andintermediate lens, and then measure the apparent ruling length on the photomicrograph. The measurement should be madeconsistently from an edge or center of one division to the corresponding edge or center of another (see Note 1). By dividing thisap
17、parent length of ruling by the known dimension of the micrometer, the magnification of the photomicrograph is determined (seeFig. 1). The accuracy of the calibration is dependent on the accuracy of the calibrated stage micrometer and the scale used tomeasure the apparent length of the photographed r
18、uling.NOTE 1The choice of using the edge or center of a reticle line depends on the method of manufacture used to produce the measuring device. Somedevices are calibrated from center to center while others are measured from one edge to another. Consult with the manufacturer to determine whichmethod
19、should be employed.5.2.2 Example 2For a metallograph with a given configuration (50X objective), determine the calibrated magnification of aphotomicrograph.5.2.2.1 Aphotograph of a stage micrometer was taken (Fig. 1).Arule was overlaid. From one corresponding edge of a divisionto another, using the
20、rule, a distance of 62 mm was measured over a known distance of 0.12 mm on the photograph of the stagemicrometer. Dividing 62 mm by 0.12 mm yields a photographic magnification of 517X.5.2.3 By photographing a stage micrometer using various combinations of objectives, intermediate lenses, zoom and be
21、llowsextensions, a table can be produced which summarizes the possible magnifications of a system.3 Microscopes incorporatingdevices allowing continuous magnification ranges (zooms) should not be used for critical measurements, except by includingreference photos of traceable reticles taken concurre
22、ntly with the measured item. Mechanical play in these devices can be asignificant source of error.5.3 Calibration for Projection Screens, Video Systems, and Video Printers: Computer Monitors:5.3.1 For projection screens that are not also photographic stations and for video computer monitors, the mag
23、nification can becalibrated as follows. Focus an image of a stage micrometer on the screen, and then measure the projected apparent length of theruling. If convenient, the measurement can be made directly on the screen, or by transferring the apparent length to a scale usingpinpoint dividers. It sho
24、uld not be assumed that a video system has the same magnification in the Virtually all modern computermonitors use square pixels, so the x(horizontal) and y(vertical) axis. Further, it should not be assumed that the ratio of themagnification in magnifications are the same provided that the monitor i
25、s displayed in its native resolution. If the xmonitordirection versus the screen resolution y direction is equal to the ratio of the dimensions of an individual pixel in the set to otherthan its native resolution, the magnifications may be different between the x and y directions. axes and result in
26、 a distorted image.3 Vander Voort, G. F., Metallography, Principles and Practice, McGraw Hill, New York, NY, 1984, pp. 279-280.NOTE 1This schematic shows the procedure used to determine the calibrated magnifications of video screens, video printers, projection screens, andphotographs.FIG. 1 Procedur
27、e for Determining Calibrated MagnificationsE1951 142The measurement should be made consistently from an edge or center of one division to the corresponding edge or center ofanother. The magnification is calculated by dividing the measured apparent length by the known dimensions of the micrometer (se
28、eExample 2 in 5.2.2 and Fig. 1).5.3.2 Magnifications of video prints should be calibrated by use of a print or prints of two measuring devices, one placed oneach axis of a single print or one placed on opposite axes on two separate prints. This calibration print should be produced at thesame magnifi
29、cation as the prints of interest. Exercise care to ensure that the aspect ratio of the object is reproduced accurately inthe print, as the x and y dimensions of the final print can be adjusted independently through the controls provided on some printers.5.3.3 Most high quality video printers will al
30、low some adjustment of the final print dimensions. Major adjustments tomagnification should be made by use of intermediate projection lenses or microscope objectives. Increasing magnification by useof video printer controls is not recommended due to the degradation of resolution.5.4 Eyepiece Microme
31、ter Calibration:5.4.1 To calibrate an eyepiece micrometer reticle, view through the eyepiece an image of a stage micrometer using a givenobjective and intermediate lens combination. Overlay the eyepiece micrometer image on the stage micrometer image, with one endof each coincident upon one another.
32、The measurement should be made consistently from an edge of one division to thecorresponding edge of another (Fig. 2). The eyepiece reticle calibration can be determined by dividing the known length of thestage micrometer by the number of overlaid eyepiece micrometer divisions. This calculation yiel
33、ds a length per division value ofthe micrometer for a given optical setup.5.4.2 Example 3For a given microscope configuration (40X objective), determine the length per division value of an eyepiecemicrometer.NOTE 1This schematic diagram illustrates the procedure used to calibrate an eyepiece measuri
34、ng reticle.FIG. 2 Diagram for Calibrating an Eyepiece Measuring ReticleE1951 1435.4.2.1 The image of the eyepiece micrometer was aligned with the stage micrometer image (Fig. 2). Eighty-five divisions werecounted over a distance of 0.21 mm on the stage micrometer. The length per division can then be
35、 calculated as follows.0.21 mm/85 divisions!1000 m/1mm!52.4752.5 m/division (3)0.21 mm85 divisions31000 m1mm 52.4752.5 m/division (3)5.4.3 Repeat the procedure listed above for various objective and intermediate lens combinations to create a table of eyepiecemicrometer calibrations.NOTE 2In order fo
36、r the magnification to be consistent from user to user, the eyepiece reticle must be focussed for the users eyes before focusingthe 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 if both eye
37、piece tubes are adjustable. Also, change in interpupillary distance may change the magnification,particularly in older microscopes.5.5 Magnification Calibration of Image Viewed Through Eyepieces:5.5.1 This procedure will give a calibrated magnification observed through the eyepieces of a particular
38、microscope lensconfiguration, independent of the user (Fig. 3).5.5.2 Focus the image of a stage micrometer through the eyepieces. This procedure will require a stage micrometer with highcontrast markings.5.5.3 Determine the position of the eyepoint of the system as follows: (1) adjust the lighting o
39、n the microscope to a maximum,(2) place an opaque or translucent piece of material perpendicular to the light path. A circular projection of the light will appear.(3) Move the material away from the eyepiece lens until the size of the circular light beam becomes a minimum. Initially, the sizeof the
40、beam will decrease until the eyepoint distance is reached, then at a distance greater than the optical eyepoint, the size ofthe 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 of viewing medium, s
41、uch as ground glass, perpendicular to the light pathat a point 250 mm plus the eyepoint distance away from the eyepiece lens. The calibration measurement can then be made directlyon the ground glass or on the developed film or resulting print. The calibration is completed by placing the divisions of
42、 a ruleNOTE 1A schematic diagram illustrating the procedure used to determine the magnification observed through the microscope eyepieces.FIG. 3 Diagram for Magnification Observed Through Microscope EyepiecesE1951 144coincident upon the projected image of the stage micrometer. The alignment should b
43、e made consistently from an edge of onedivision to the corresponding edge of another. (A large-format bellows camera, without lens, may be conveniently used here. Ifthis is done, a film of the image can also be exposed, with the calibration then performed on the developed film.)5.5.5 Determine the o
44、bserved magnification by dividing the measured length of the projected section of the stage micrometerby the known length of that section of the stage micrometer.5.5.6 Repeat this procedure for various objective and intermediate lens combinations to create a table of observablemagnifications.5.5.7 E
45、xample 4Determine the magnification viewed through an eyepiece with a microscope configuration consisting of a10X objective and a 10X eyepiece.5.5.7.1 Using an overhead transparency, and a rule placed perpendicular to the plane of the eyepiece lens, the eyepoint wasdetermined to be at a distance of
46、18 mm. Next, a distance of 268 mm was measured perpendicular from the plane of the eyepiece.5.5.7.2 A viewing medium was fixed at this distance parallel to the plane of the eyepiece lens. The divisions of a rule wereplaced coincident upon the projected image of the stage micrometer consistently from
47、 an edge of one division to the correspondingedge of another. A distance of 89 mm was measured over a known distance of 0.9 mm on the stage micrometer. By dividing themeasured length by the known length a calibrated magnification of 99X was determined.5.6 Filar Eyepiece Calibration:5.6.1 The calibra
48、tion of a filar measuring eyepiece is similar to that of an eyepiece reticle as illustrated in Fig. 2. The moveablecross-hair in the eyepiece is positioned at an extreme end of a stage micrometer coincident with one micrometer division. Themeasurement should be made consistently from an edge or the
49、center of one division to another.5.6.2 For a drum filar eyepiece, note the micrometer drum value. Traverse the cross-hair over as many micrometer divisions aspossible that are visible in the central region of the field of view. Note the new micrometer drum value. To obtain the total drummovement, subtract the final drum value from the initial value. The value of each increment on the filar drum is determined bydividing the actual length traversed on the stage micrometer by the total drum movement. Repeat this procedure for each objectiveof interest. This
