Linear Measurements (Micrometry)
The first reported measurements performed with an optical microscope were undertaken in the late 1600s by the Dutch scientist Antonie van Leeuwenhoek, who used fine grains of sand as a gauge to determine the size of human erythrocytes. Since then, countless approaches have been employed for measuring linear, area, and volume specimen dimensions with the microscope (a practice known as micrometry or morphometrics), and a wide variety of useful techniques have emerged over the past few hundred years.
Introduction to Micrometry - Performing measurements at high magnifications in compound optical microscopy is generally conducted by the application of eyepiece reticles in combination with stage micrometers. A majority of measurements made with compound microscopes fall into the size range of 0.2 micrometers to 25 millimeters (the average field diameter of widefield eyepieces). Horizontal distances below 0.2 micrometers are beneath the resolving power of the microscope, and lengths larger than the field of view of a widefield eyepiece are usually (and far more conveniently) measured with a stereomicroscope.
Interactive Java Tutorials
Eyepiece Reticle Calibration - Calibration of an eyepiece reticle (determination of the micrometer graduation relationship) for a particular objective is typically conducted by following standard recommended procedures. Note that calibration of an eyepiece reticle holds only for the specific objective/eyepiece combination being tested, and for the mechanical tube length of the microscope. This interactive tutorial explores calibration of various eyepiece reticles with a stage micrometer, and demonstrates how the reticle can then be employed to determine linear specimen dimensions.
Selected Literature References
Reference Listing - In addition to basic linear measurements, the optical microscope is often employed to measure the area or volume of a specimen and for counting particles and fibers. Several books and review articles focused on micrometry and stereology been published by leading researchers in the field and were utilized as references to prepare the measurement discussions included in the MicroscopyU website. This section contains periodical location information about these articles, as well as providing a listing of selected review articles and books describing quantitative microscopy.
Matthew J. Parry-Hill, Thomas J. Fellers and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.
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