ASTM E1951-98

Standard Guide for Calibrating Reticles and Light Microscope Magnifications

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 problems, 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: 09-Dec-2001
• ICS: 37.020 - Optical equipment
• Technical Committee: E04 - Metallography
• Drafting Committee: E04.03 - Light Microscopy

Relations

• Replaced By: ASTM E1951-01 - Standard Guide for Calibrating Reticles and Light Microscope Magnifications
• Effective Date: 10-Dec-2001
• Referred By: ASTM E883-11(2017) - Standard Guide for Reflected–Light Photomicrography
• Effective Date: 10-Dec-2001
• 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: 10-Dec-2001
• Referred By: ASTM E45-18a - Standard Test Methods for Determining the Inclusion Content of Steel
• Effective Date: 10-Dec-2001
• Referred By: ASTM E1077-14(2021) - Standard Test Methods for Estimating the Depth of Decarburization of Steel Specimens
• Effective Date: 10-Dec-2001

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E 1951 – 98
Standard Guide for
Calibrating Reticles and Light Microscope Magnifications
This standard is issued under the fixed designation E 1951; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope supplied ratings, is only an approximation of the true magni-
fication, since individual optical components may vary from
1.1 This guide covers methods for calculating and calibrat-
their marked magnification. For a precise determination of the
ing microscope magnifications, photographic magnifications,
magnification observed through an eyepiece, see the procedure
video monitor magnifications, grain size comparison reticles,
describe in 5.5.
and other measuring reticles. Reflected light microscopes are
5.1.2 For a compound microscope, the total magnification
used to characterize material microstructures. Many materials
(M ) of an image through the eyepiece is the product of the
t
engineering decisions may be based on qualitative and quan-
objective lens magnification (M ), the eyepiece magnification
titative analyses of a microstructure. It is essential that micro- o
(M ), and, if present, a zoom system or other intermediate lens
e
scope magnifications and reticle dimensions be accurate.
magnification (M ). An expression for the total magnification is
1.2 The calibration using these methods is only as precise as i
shown in Eq 1.
the measuring devices used. It is recommended that the stage
micrometer or scale used in the calibration should be traceable M 5 M 3 M 3 M (1)
t o e i
to the National Institute of Standards and Technology (NIST)
5.1.3 Example 1—For a microscope configured with a 10X
or a similar organization.
objective, a 10X eyepiece, and a 1.25X intermediate lens, the
1.3 This standard does not purport to address all of the
total magnification observed through the eyepiece would be
safety concerns, if any, associated with its use. It is the
calculated as follows.
responsibility of the user of this standard to establish appro-
M 5 10 10 1.25 5 125 (2)
~ !~ !~ !
t
priate safety and health practices and determine the applica-
5.2 Calibration for Photomicrography Magnifications:
bility of regulatory limitations prior to use.
5.2.1 The magnification of an image can be determined by
2. Referenced Documents
photographing a calibrated stage micrometer using the desired
optical setup. First, photograph the stage micrometer using the
2.1 ASTM Standards:
desired combination of objective, bellows extension, zoom and
E 7 Terminology Relating to Metallography
intermediate lens, and then measure the apparent ruling length
E 112 Test Methods for Determining Average Grain Size
on the photomicrograph. The measurement should be made
3. Terminology
consistently from an edge or center of one division to the
3.1 Definitions—All terms used in this guide are defined in corresponding edge or center of another (see Note 1). By
Terminology E 7. dividing this apparent length of ruling by the known dimension
of the micrometer, the magnification of the photomicrograph is
4. Significance and Use
determined (see Fig. 1). The accuracy of the calibration is
4.1 These methods can be used to determine magnifications dependent on the accuracy of the calibrated stage micrometer
as viewed through the eyepieces of light microscopes.
and the scale used to measure the apparent length of the
4.2 These methods can be used to calibrate microscope photographed ruling.
magnifications for photography, video systems, and projection
NOTE 1—The choice of using the edge or center of a reticle line
stations.
depends on the method of manufacture used to produce the measuring
4.3 Reticles may be calibrated as independent articles and as
device. Some devices are calibrated from center to center while others are
components of a microscope system.
measured from one edge to another. Consult with the manufacturer to
determine which method should be employed.
5. Procedures
5.2.2 Example 2—For a metallograph with a given configu-
5.1 Nominal Magnification Calculations:
ration (50X objective), determine the calibrated magnification
5.1.1 A calculated magnification, using the manufacturer’s
of 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 a
This guide is under the jurisdiction of ASTM Committee E04 on Metallography
and is the direct responsibility of Subcommittee E04.03 on Light Microscopy.
division to another, using the rule, a distance of 62 mm was
Current edition approved May 10, 1998. Published August 1998.
measured over a known distance of 0.12 mm on the photograph
Annual Book of ASTM Standards, Vol 03.01.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 1951
NOTE 1—This schematic shows the procedure used to determine the calibrated magnifications of video screens, video printers, projection screens, and
photographs.
FIG. 1 Procedure for Determining Calibrated Magnifications
of the stage micrometer. Dividing 62 mm by 0.12 mm yields a to ensure that the aspect ratio of the object is reproduced
photographic magnification of 517X. accurately in the print, as the x and y dimensions of the final
5.2.3 By photographing a stage micrometer using various print can be adjusted independently through the controls
combinations of objectives, intermediate lenses, zoom and provided on some printers.
bellows extensions, a table can be produced which summarizes
5.3.3 Most high quality video printers will allow some
the possible magnifications of a system. Microscopes incor-
adjustment of the final print dimensions. Major adjustments to
porating devices allowing continuous magnification ranges
magnification should be made by use of intermediate projec-
(zooms) should not be used for critical measurements, except
tion lenses or microscope objectives. Increasing magnification
by including reference photos of traceable reticles taken
by use of video printer controls is not recommended due to the
concurrently with the measured item. Mechanical play in these degradation of resolution.
devices can be a significant source of error.
5.4 Eyepiece Micrometer Calibration:
5.3 Calibration for Projection Screens, Video Systems, and
5.4.1 To calibrate an eyepiece micrometer reticle, view
Video Printers:
through the eyepiece an image of a stage micrometer using a
5.3.1 For projection screens that are not also photographic
given objective and intermediate lens combination. Overlay the
stations and for video monitors, the magnification can be
eyepiece micrometer image on the stage micrometer image,
calibrated as follows. Focus an image of a stage micrometer on
with one end of each coincident upon one another. The
the screen, and then measure the projected apparent length of
measurement should be made consistently from an edge of one
the ruling. If convenient, the measurement can be made
division to the corresponding edge of another (Fig. 2). The
directly on the screen, or by transferring the apparent length to
eyepiece reticle calibration can be determined by dividing the
a scale using pinpoint dividers. It should not be assumed that a
known length of the stage micrometer by the number of
video system has the same magnification in the x (horizontal)
overlaid eyepiece micrometer divisions. This calculation yields
and y (vertical) axis. Further, it should not be assumed that the
a length per division value of the micrometer for a given
same x:y ratio exists on the screen as in pixel representation.
optical setup.
The measurement should be made consistently from an edge or
5.4.2 Example 3—For a given microscope configuration
center of one division to the corresponding edge or center of
(40X objective), determine the length per division value of an
another. The magnification is calculated by dividing the mea-
eyepiece micrometer.
sured apparent length by the known dimensions of the mi-
5.4.2.1 The image of the eyepiece micrometer was aligned
crometer (see Example 2 in Section 5.1.3 and Fig. 1).
with the stage micrometer image (Fig. 2). Eighty-five divisions
5.3.2 Magnifications of video prints should be calibrated by
were counted over a distance of 0.21 mm on the stage
use of a print of two measuring devices, one placed on each
micrometer. The length per division can then be calculated as
axis of the print. This calibration print should be produced at
follows.
the same magnification as the prints of interest. Exercise care
~0.21 mm / 85 divisions! ~1000 μm/1mm! 5 2.4752.5 μm/division
(3)
3 5.4.3 Repeat the procedure listed above for various objec-
Vander Voort, G. F., Metallography, Principles and Practice, McGraw Hill, New
York, NY, 1984, pp. 279-280. tive and intermediate lens combinations to create a table of
E 1951
NOTE 1—This schematic diagram illustrates the procedure used to calibrate an eyepiece measuring reticle.
FIG. 2 Diagram for Calibrating an Eyepiece Measuring Reticle
eyepiece micrometer calibrations. 5.5.4 Place an unexposed piece of film or a rigid piece of
viewing medium, such as ground glass, perpendicular to the
NOTE 2—In order for the magnification to be consistent from user to
light path at a point 250 mm plus the eyepoint distance away
user, the eyepiece reticle must be focussed for the user’s eyes before
from the eyepiece lens. The calibration measurement can then
focusing the microscope on the image as produced by the objective. Also,
the positioning of the reticle in the eyepiece must be repeatable. be made directly on the ground glass or on the developed film
NOTE 3—Caution must be observed if both eyepiece tubes are adjust-
or resulting print. The calibration is completed by placing the
able. Also, change in interpupillary distance may change the magnifica-
divisions of a rule coincident upon the projected image of the
tion, particularly in older microscopes.
stage micrometer. The alignment should be made consistently
5.5 Magnification Calibration of Image Viewed Through
from an edge of one division to the corresponding edge of
Eyepieces:
another.
5.5.1 This procedure will give a calibrated magnification
5.5.5 Determine the observed magnification by dividing the
observed through the eyepieces of a particular microscope lens
measured length of the projected section of the stage microme-
configuration, independent of the user (Fig. 3).
ter by the known length of that section of the stage micrometer.
5.5.2 Focus the image of a stage micrometer through the
5.5.6 Repeat this procedure for various objective and inter-
eyepieces. This procedure will require a stage micrometer with
mediate lens combinations to create a table of observable
high contrast markings.
magnifications.
5.5.3 Determine the position of the eyepoint of the system
5.5.7 Example 4—Determine the magnification viewed
as follows: (1) adjust the lighting on the microscope to a
through an eyepiece with a microscope configuration consist-
maximum, (2) place an opaque or translucent piece of material
ing of a 10X objective and a 10X eyepiece.
perpendicular to the light path. A circular projection of the light
5.5.7.1 Using an overhead transparency, and a rule placed
will appear. (3) Move the material away from the eyepiece lens
perpendicular to the plane of the eyepiece lens, the eyepoint
until the size of the circular light beam becomes a minimum.
was determined to be at a distance of 18 mm. Next, a distance
Initially, the size of the beam will decrease until the eyepoint
of 268 mm was measured perpendicular from the plane of the
distance is reached, then at a distance greater than the optical
eyepiece.
eyepoint, the size of the circular projection will increase. (4)
Note the distance of the eyepoint from the eyepiece lens. 5.5.7.2 A viewing medium was fixed at this distance parallel
E 1951
NOTE 1—A schematic diagram illustrating the procedure used to determine the magnification observed through the microscope eyepieces.
FIG. 3 Diagram for Magnification Observed Through Microscope Eyepieces
to the plane of the eyepiece lens. The divisions of a rule were determining an eyepiece micrometer calibration ( Example 3 in
placed coincident upon the projected image of the stage Section 5.4.2.1).
micrometer consistently from an edge of one division to the
5.6.3 For digital filar eyepieces, a multiplier must by deter-
corresponding edge of another. A distance of 89 mm was mined for each objective.
measured over a known distance of 0.9 mm on the stage
5.6.3.1 To determine the value of the multiplier for a
micrometer. By dividing the measured length by the known specific microscope configuration, set the multiplier to one, and
length a calibrated magnification of 99X was determined.
traverse a known distance.
5.6 Filar Eyepiece Calibration:
5.6.3.2 The value of the multiplier is determined by dividing
5.6.1 The calibration of a filar measuring eyepiece is similar the known distance traversed by the value determined by the
filar eyepiece.
to that of an eyepiece reticle as illustrated in Fig. 2. The
moveable cross-hair in the eyepiece is positioned at an extreme 5.6.3.3 Next, set the instrument to zero, and enter the
end of a stage micrometer coincident with one micrometer approximate multiplier into the system. Traverse the stage
division. The measurement should be made consistently from micrometer as described in the previous section. If the mea-
an edge or the center of one division to another. sured distance is incorrect, adjust the multiplier accordingly.
Reset to zero, and traverse the stage micrometer again.
5.6.2 For a drum filar eyepiece, note the micrometer drum
value. Traverse the crosshair over as many micrometer divi- 5.6.3.4 Repeat these steps until an accurate multiplier has
been determined for each objective.
sions visible in the central region of the field of view. Note the
new micrometer drum value. To obtain the total drum move- 5.6.3.5 Example 5—Determine the digital filar eyepiece
ment, subtract the final drum value from the initial value. The multiplier for a given microscope configuration. (50X objec-
value of each increment on the filar drum is determined by tive). After setting the multiplier to 1, a distance of 250 μm was
dividing the actual length traversed on the stage micrometer by traversed along an image of a stage micrometer. The filar
the total drum movement. Repeat this procedure for each eyepiece measured 17 698. The multiplier was then determined
objective of interest. This calculation is similar to that of by dividing 2
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