ASTM E1951-02(2007)

Standard Guide for Calibrating Reticles and Light Microscope Magnifications

SIGNIFICANCE AND USE
These methods can be used to determine magnifications as viewed through the eyepieces of light microscopes.
These methods can be used to calibrate microscope magnifications for photography, video systems, and projection stations.
Reticles may be calibrated as independent articles and as components of a microscope system.
SCOPE
1.1 This guide covers methods for calculating and calibrating microscope magnifications, photographic magnifications, video monitor magnifications, grain size comparison reticles, and other measuring reticles. Reflected light microscopes are used to characterize material microstructures. Many materials engineering decisions may be based on qualitative and quantitative analyses of a microstructure. It is essential 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 stage micrometer or scale used in the calibration should be traceable to the National Institute of Standards and Technology (NIST) or a 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 responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 30-Sep-2007
• ICS: 37.020 - Optical equipment
• Technical Committee: E04 - Metallography
• Drafting Committee: E04.03 - Light Microscopy

Relations

• Replaces: ASTM E1951-02 - Standard Guide for Calibrating Reticles and Light Microscope Magnifications
• Effective Date: 01-Oct-2007
• Referred By: ASTM E45-18a - Standard Test Methods for Determining the Inclusion Content of Steel
• Effective Date: 01-Oct-2007
• Referred By: ASTM D7416-09(2020) - Standard Practice for Analysis of In-Service Lubricants Using a Particular Five-Part (Dielectric Permittivity, Time-Resolved Dielectric Permittivity with Switching Magnetic Fields, Laser Particle Counter, Microscopic Debris Analysis, and Orbital Viscometer) Integrated Tester
• Effective Date: 01-Oct-2007
• Referred By: ASTM E1077-14(2021) - Standard Test Methods for Estimating the Depth of Decarburization of Steel Specimens
• Effective Date: 01-Oct-2007
• Referred By: ASTM E883-11(2017) - Standard Guide for Reflected–Light Photomicrography
• Effective Date: 01-Oct-2007

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:E1951 −02(Reapproved 2007)
Standard Guide for
Calibrating Reticles and Light Microscope Magnifications
This standard is issued under the fixed designation E1951; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 4.3 Reticlesmaybecalibratedasindependentarticlesandas
components of a microscope system.
1.1 This guide covers methods for calculating and calibrat-
ing microscope magnifications, photographic magnifications,
5. Procedures
video monitor magnifications, grain size comparison reticles,
5.1 Nominal Magnification Calculations:
and other measuring reticles. Reflected light microscopes are
5.1.1 A calculated magnification, using the manufacturer’s
used to characterize material microstructures. Many materials
supplied ratings, is only an approximation of the true
engineering decisions may be based on qualitative and quan-
magnification, since individual optical components may vary
titative analyses of a microstructure. It is essential that micro-
from their marked magnification. For a precise determination
scope magnifications and reticle dimensions be accurate.
of the magnification observed through an eyepiece, see the
1.2 Thecalibrationusingthesemethodsisonlyaspreciseas
procedure describe in 5.5.
the measuring devices used. It is recommended that the stage
5.1.2 For a compound microscope, the total magnification
micrometer or scale used in the calibration should be traceable
(M) of an image through the eyepiece is the product of the
t
to the National Institute of Standards and Technology (NIST)
objective lens magnification (M ), the eyepiece magnification
o
or a similar organization.
(M ), and, if present, a zoom system or other intermediate lens
e
1.3 This standard does not purport to address all of the
magnification (M).An expression for the total magnification is
i
safety concerns, if any, associated with its use. It is the
shown in Eq 1.
responsibility of the user of this standard to establish appro-
M 5 M 3M 3M (1)
t o e i
priate safety and health practices and determine the applica-
5.1.3 Example 1—For a microscope configured with a 10X
bility of regulatory limitations prior to use.
objective, a 10X eyepiece, and a 1.25X intermediate lens, the
2. Referenced Documents
total magnification observed through the eyepiece would be
2.1 ASTM Standards:
calculated as follows.
E7 Terminology Relating to Metallography
M 5 10 10 1.25 5 125 (2)
~ !~ !~ !
t
E112 Test Methods for Determining Average Grain Size
5.2 Calibration for Photomicrography Magnifications:
3. Terminology
5.2.1 The magnification of an image can be determined by
photographing a calibrated stage micrometer using the desired
3.1 Definitions—All terms used in this guide are defined in
optical setup. First, photograph the stage micrometer using the
Terminology E7.
desired combination of objective, bellows extension, zoom and
4. Significance and Use
intermediate lens, and then measure the apparent ruling length
on the photomicrograph. The measurement should be made
4.1 These methods can be used to determine magnifications
consistently from an edge or center of one division to the
as viewed through the eyepieces of light microscopes.
corresponding edge or center of another (see Note 1). By
4.2 These methods can be used to calibrate microscope
dividing this apparent length of ruling by the known dimension
magnifications for photography, video systems, and projection
of the micrometer, the magnification of the photomicrograph is
stations.
determined (see Fig. 1). The accuracy of the calibration is
dependent on the accuracy of the calibrated stage micrometer
This guide is under the jurisdiction ofASTM Committee E04 onMetallography
and the scale used to measure the apparent length of the
and is the direct responsibility of Subcommittee E04.03 on Light Microscopy.
Current edition approved Oct. 1, 2007. Published October 2007. photographed ruling.
Originally approved in 1998. Last previous edition approved in 2002 as
NOTE1—Thechoiceofusingtheedgeorcenterofareticlelinedepends
E1951–02. DOI: 10.1520/E1951-02R07.
on the method of manufacture used to produce the measuring device.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Some devices are calibrated from center to center while others are
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on measured from one edge to another. Consult with the manufacturer to
the ASTM website. determine which method should be employed.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1951−02 (2007)
NOTE 1—This schematic shows the procedure used to determine the calibrated magnifications of video screens, video printers, projection screens, and
photographs.
FIG. 1Procedure for Determining Calibrated Magnifications
5.2.2 Example 2—For a metallograph with a given configu- corresponding edge or center of another. The magnification is
ration (50X objective), determine the calibrated magnification calculated by dividing the measured apparent length by the
of a photomicrograph. known dimensions of the micrometer (see Example 2 in 5.2.2
5.2.2.1 Aphotograph of a stage micrometer was taken (Fig. and Fig. 1).
1). A rule was overlaid. From one corresponding edge of a
5.3.2 Magnifications of video prints should be calibrated by
division to another, using the rule, a distance of 62 mm was
useofaprintorprintsoftwomeasuringdevices,oneplacedon
measuredoveraknowndistanceof0.12mmonthephotograph
each axis of a single print or one placed on opposite axes on
of the stage micrometer. Dividing 62 mm by 0.12 mm yields a
two separate prints. This calibration print should be produced
photographic magnification of 517X.
atthesamemagnificationastheprintsofinterest.Exercisecare
5.2.3 By photographing a stage micrometer using various
to ensure that the aspect ratio of the object is reproduced
combinations of objectives, intermediate lenses, zoom and
accurately in the print, as the x and y dimensions of the final
bellows extensions, a table can be produced which summarizes
print can be adjusted independently through the controls
the possible magnifications of a system. Microscopes incor-
provided on some printers.
porating devices allowing continuous magnification ranges
5.3.3 Most high quality video printers will allow some
(zooms) should not be used for critical measurements, except
adjustment of the final print dimensions. Major adjustments to
by including reference photos of traceable reticles taken
magnification should be made by use of intermediate projec-
concurrently with the measured item. Mechanical play in these
tion lenses or microscope objectives. Increasing magnification
devices can be a significant source of error.
by use of video printer controls is not recommended due to the
5.3 Calibration for Projection Screens, Video Systems, and
degradation of resolution.
Video Printers:
5.4 Eyepiece Micrometer Calibration:
5.3.1 For projection screens that are not also photographic
5.4.1 To calibrate an eyepiece micrometer reticle, view
stations and for video monitors, the magnification can be
through the eyepiece an image of a stage micrometer using a
calibrated as follows. Focus an image of a stage micrometer on
givenobjectiveandintermediatelenscombination.Overlaythe
the screen, and then measure the projected apparent length of
eyepiece micrometer image on the stage micrometer image,
the ruling. If convenient, the measurement can be made
with one end of each coincident upon one another. The
directly on the screen, or by transferring the apparent length to
measurement should be made consistently from an edge of one
a scale using pinpoint dividers. It should not be assumed that a
video system has the same magnification in the x (horizontal) division to the corresponding edge of another (Fig. 2). The
eyepiece reticle calibration can be determined by dividing the
and y (vertical) axis. Further, it should not be assumed that the
ratio of the magnification in the x direction versus the y known length of the stage micrometer by the number of
overlaid eyepiece micrometer divisions.This calculation yields
directionisequaltotheratioofthedimensionsofanindividual
pixel in the x and y directions. The measurement should be a length per division value of the micrometer for a given
optical setup.
made consistently from an edge or center of one division to the
5.4.2 Example 3—For a given microscope configuration
(40X objective), determine the length per division value of an
VanderVoort,G.F.,Metallography,PrinciplesandPractice,McGrawHill,New
York, NY, 1984, pp. 279-280. eyepiece micrometer.
E1951−02 (2007)
NOTE 1—This schematic diagram illustrates the procedure used to calibrate an eyepiece measuring reticle.
FIG. 2Diagram for Calibrating an Eyepiece Measuring Reticle
5.4.2.1 The image of the eyepiece micrometer was aligned 5.5 Magnification Calibration of Image Viewed Through
with the stage micrometer image (Fig. 2). Eighty-five divisions
Eyepieces:
were counted over a distance of 0.21 mm on the stage
5.5.1 This procedure will give a calibrated magnification
micrometer. The length per division can then be calculated as
observed through the eyepieces of a particular microscope lens
follows.
configuration, independent of the user (Fig. 3).
0.21 mm/85 divisions 1000 µm/1 mm 5 2.47 5 2.5 µm/division
~ !~ !
5.5.2 Focus the image of a stage micrometer through the
(3)
eyepieces. This procedure will require a stage micrometer with
high contrast markings.
5.4.3 Repeat the procedure listed above for various objec-
5.5.3 Determine the position of the eyepoint of the system
tive and intermediate lens combinations to create a table of
eyepiece micrometer calibrations. as follows: (1) adjust the lighting on the microscope to a
maximum, (2) place an opaque or translucent piece of material
NOTE 2—In order for the magnification to be consistent from user to
perpendiculartothelightpath.Acircularprojectionofthelight
user, the eyepiece reticle must be focussed for the user’s eyes before
focusing the microscope on the image as produced by the objective.Also,
will appear. (3) Move the material away from the eyepiece lens
the positioning of the reticle in the eyepiece must be repeatable.
until the size of the circular light beam becomes a minimum.
NOTE 3—Caution must be observed if both eyepiece tubes are adjust-
Initially, the size of the beam will decrease until the eyepoint
able. Also, change in interpupillary distance may change the
distance is reached, then at a distance greater than the optical
magnification, particularly in older microscopes.
E1951−02 (2007)
NOTE 1—A schematic diagram illustrating the procedure used to determine the magnification observed through the microscope eyepieces.
FIG. 3Diagram for Magnification Observed Through Microscope Eyepieces
eyepoint, the size of the circular projection will increase. (4) 5.5.7.1 Using an overhead transparency, and a rule placed
Note the distance of the eyepoint from the eyepiece lens. perpendicular to the plane of the eyepiece lens, the eyepoint
5.5.4 Place an unexposed piece of film or a rigid piece of was determined to be at a distance of 18 mm. Next, a distance
viewing medium, such as ground glass, perpendicular to the of 268 mm was measured perpendicular from the plane of the
light path at a point 250 mm plus the eyepoint distance away eyepiece.
from the eyepiece lens. The calibration measurement can then
5.5.7.2 Aviewingmediumwasfixedatthisdistanceparallel
be made directly on the ground glass or on the developed film
to the plane of the eyepiece lens. The divisions of a rule were
or resulting print. The calibration is completed by placing the
placed coincident upon the projected image of the stage
divisions of a rule coincident upon the projected image of the
micrometer consistently from an edge of one division to the
stage micrometer. The alignment should be made consistently
corresponding edge of another. A distance of 89 mm was
from an edge of one division to the corresponding edge of
measured over a known distance of 0.9 mm on the stage
another. (Alarge-format bellows camera, without lens, may be
micrometer. By dividing the measured length by the known
conveniently used here. If this is done, a film of the image can
length a calibrated magnification of 99X was determined.
also be exposed, with the calibration then performed on the
5.6 Filar Eyepiece Calibration:
developed film.)
5.6.1 The calibration of a filar measuring eyepiece is similar
5.5.5 Determine the observed magnification by dividing the
to that of an eyepiece reticle as illustrated in Fig. 2. The
measured length of the projected section of the stage microm-
moveable cross-hair in the eyepiece is positioned at an extreme
eter by the known length of that section of the stage microm-
end of a stage micrometer coincident with one micrometer
eter.
division. The measurement should be made consistently from
5.5.6 Repeat this procedure for various objective and inter-
an edge or the center of one division to another.
mediate lens combinations to create a table of observable
magnifications. 5.6.2 For a drum filar eyepiece, note the micrometer drum
5.5.7 Example 4—Determine the magnification viewed value. Traverse the cross-hair over as many micrometer divi-
through an eyepiece with a microscope configuration consist- sions as possible that are visible in the central region of the
ing of a 10X objective and a 10X eyepiece. field of view. Note the new micrometer drum value. To obtain
E1951−02 (2007)
the total drum movement, subtract the final drum value from 5.6.4 For more specific calibration procedures for digital
the initial value. The value of each increment on the filar drum filar eyepieces, see the manufacturer’s instruction manual.
is determined by dividing the actual length traversed on the
5.7 Grain Size Comparison Rectile Calibration:
stage micrometer by the total drum movement. Repeat this
5.7.1 A grain size reticle consists of a series of figures,
procedure for each objective of interest. This calculation is
representing various grain sizes, which allow an operator to
similar to that of determining an eyepiece micrometer calibra-
conveniently determine the grain size of a specimen according
tion ( Example 3 in Section 5.4.2.1).
to Test Methods E112 comparison method (
...