petrographic microscope parts and functions pdf

Petrographic Microscope Parts And Functions Pdf

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The petrographic, or polarizing, microscope, a compound instrument using plane-polarized transmitted light, has been applied for over a hundred years as a standard tool in the examination of rock textures and optical properties of minerals. Microscopes using reflected light are also available for the examination of opaque minerals.

Relatively few of us are lucky enough to have and use a wide range of makes and models of microscopes. Work-place microscope labs often have little variety in brands or models, so as to reduce costs for maintenance and accessories. But because I have moved around a few times since the early s, different microscopes have been available for my geological field research and education. An enjoyable if challenging task in the s was teaching optical mineralogy and petrography with polarizing microscopes pol scopes , in advanced undergraduate courses in academic geology programs. In recent years, I have been servicing, refurbishing, and selling microscopes in a part-time business.

Polarizing microscopy

A petrographic microscope is a type of optical microscope used in petrology and optical mineralogy to identify rocks and minerals in thin sections. The microscope is used in optical mineralogy and petrography , a branch of petrology which focuses on detailed descriptions of rocks. The method is called " polarized light microscopy " PLM. Depending on the grade of observation required, petrological microscopes are derived from conventional brightfield microscopes of similar basic capabilities by:. Petrographic microscopes are constructed with optical parts that do not add unwanted polarizing effects due to strained glass, or polarization by reflection in prisms and mirrors. These special parts add to the cost and complexity of the microscope.

Petrographic microscope

One of the wonders of the scientific world is that so much of what goes on is invisible to the naked eye. Invented in by a Dutch optician named Zacharias Janssen, the compound or light microscope gives students and scientists a close-up view of tiny structures like cells and bacteria. Read on to find out more about microscope parts and how to use them. The eyepiece contains the ocular lens, which the user looks through to see the magnified specimen. The ocular lens has a magnification that can range from 5x to 30x, but 10x or 15x is the most common setting. The eyepiece tube connects the eyepiece and ocular lens to the objective lenses located near the microscope stage.

Polarized light is a contrast-enhancing technique that improves the quality of the image obtained with birefringent materials when compared to other techniques such as darkfield and brightfield illumination, differential interference contrast, phase contrast, Hoffman modulation contrast, and fluorescence. Polarized light microscopes have a high degree of sensitivity and can be utilized for both quantitative and qualitative studies targeted at a wide range of anisotropic specimens. Qualitative polarizing microscopy is very popular in practice, with numerous volumes dedicated to the subject. In contrast, the quantitative aspects of polarized light microscopy, which is primarily employed in crystallography, represent a far more difficult subject that is usually restricted to geologists, mineralogists, and chemists. However, steady advances made over the past few years have enabled biologists to study the birefringent character of many anisotropic sub-cellular assemblies. The polarized light microscope is designed to observe and photograph specimens that are visible primarily due to their optically anisotropic character. In order to accomplish this task, the microscope must be equipped with both a polarizer , positioned in the light path somewhere before the specimen, and an analyzer a second polarizer; see Figure 1 , placed in the optical pathway between the objective rear aperture and the observation tubes or camera port.


The Condenser and Substage Assembly. The parts of the microscope that are located above the base but below the stage are called the substage assembly. The substage assembly includes the condenser, the lower polarizer, light filters, and diaphragms.


Petrographic Microscope Parts And Functions Pdf

This section provides an overview of the parts of a petrographic microscope and what each part does. It is also a good review for a student who has used a petrographic microscope in a previous class but needs a refresher on the anatomy of a microscope. Look at the diagrams of the petrographic microscope and its parts in Figures 4. List all that you feel you completely understand how to use here:.

The polarized light microscope is designed to observe and photograph specimens that are visible primarily due to their optically anisotropic character. In order to accomplish this task, the microscope must be equipped with both a polarizer , positioned in the light path somewhere before the specimen, and an analyzer a second polarizer , placed in the optical pathway between the objective rear aperture and the observation tubes or camera port. Image contrast arises from the interaction of plane-polarized light with a birefringent or doubly-refracting specimen to produce two individual wave components that are each polarized in mutually perpendicular planes. The velocities of these components are different and vary with the propagation direction through the specimen. After exiting the specimen, the light components become out of phase with each other, but are recombined with constructive and destructive interference when they pass through the analyzer.

In this section, we explore the parts of the petrographic or polarizing light microscope. This section is appropriate for students who have no prior experience with using microscopes. What does a microscope look like?

Microscopy U - The source for microscopy education

Previous Table of Contents Next. A petrographic microscope, also called a polarizing microscope , is best described as a compound, transmitted-light microscope to which components have been added to enable the determination of the optical properties of translucent substances.

2.4 Parts of the Petrographic Microscope

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Below is a brief explanation of the more important parts of the microscope: 1. Eyepiece: this is the lens that you look through at the top of the microscope. 2.


Optical Mineralogy and Petrography

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2 Comments

  1. Campbell L.

    This type of microscope differs from the normal one by using a polarized light, in which the light waves vibrate in one direction.

    20.11.2020 at 20:30 Reply
  2. Olivie R.

    Key Terms. Eyepiece. Viewing tube. Bertrand lens. Analyzer. Accessory plate. Revolving nosepiece. Objective. Rotating stage with goniometer.

    28.11.2020 at 13:24 Reply

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