ASTM_E_1951_-_14.pdf

Designation:E195114Standard 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,the 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 calibrat-ing microscope magnifications,photographic magnifications,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 that 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 Technology(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 limitations 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 determine 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.Procedures5.1 Nominal Magnification Calculations:5.1.1 A calculated magnification,using the manufacturerssupplied ratings,is only an approximation of the truemagnification,since individual optical components may varyfrom their marked magnification.For a precise determinationof the magnification observed through an eyepiece,see theprocedure 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 theobjective lens magnification(Mo),the eyepiece magnification(Me),and,if present,a zoom system or other intermediate lensmagnification(Mi).An expression for the total magnification isshown in Eq 1.Mt5 Mo3Me3Mi(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 1031031.255 125(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,zoom 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 dimensionof 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.NOTE1The choice of using the edge or center of a reticle line dependson the method of manufacture used to produce the measuring device.Some devices are calibrated from center to center while others aremeasured from one edge to another.Consult with the manufacturer todetermine which method should be employed.1This guide is under the jurisdiction ofASTM Committee E04 on Metallographyand is the direct responsibility of Subcommittee E04.03 on Light Microscopy.Current edition approved Nov.1,2014.Published December 2014.Originallyapproved in 1998.Last previous edition approved in 2007 as E195102(2007).DOI:10.1520/E1951-14.2For referenced ASTM standards,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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 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