Petrographic Microscope Parts And Functions Pdf
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- Polarizing microscopy
- Petrographic Microscope Parts And Functions Pdf
- Petrographic microscope
- Parts of the Microscope and Their Uses
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. Polarization of light in modern microscopes is achieved by a synthetic material made of a plastic film containing a mass of fine-grained prismatic crystals of herapathite a complex sulfate and iodide of quinine with a parallel orientation.
This type of microscope differs from the normal one by using a polarized light, in which the light waves vibrate in one direction. Unlike the ones from normal light that vibrate in random directions. When studying a specimen the light has to pass through a polarizer polarizing filter and then in some cases through an analyzer — to increase the quality of image contrast. A polarizing microscope can be obtain from a compound or a normal one by adding some pieces.
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. The designation of the microscope as a compound microscope indicates that it has an ocular that focuses on a virtual image of the subject produced in the tube of the microscope by the objective lens. The professional petrographic microscope has a substage condenser that can be centered and focused. The substage has field and aperture diaphragms. The polarizing components are the upper and lower polarizing devices, the Bertrand lens and its mounting between the upper polarizing device and the ocular , an accessory flip-in lens for convergent light mounted as the top element of the condenser, and a graduated rotating stage with a removable click stop that can be activated to indicate a degree rotation from any selected direction.
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. When an anisotropic specimen is brought into focus and rotated through degrees on a circular polarized light microscope stage, it will sequentially appear bright and dark extinct , depending upon the rotation position. When the specimen long axis is oriented at a degree angle to the polarizer axis, the maximum degree of brightness will be achieved, and the greatest degree of extinction will be observed when the two axes coincide.
Petrographic Microscope Parts And Functions Pdf
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.
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.
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. The microscope arm connects the eyepiece tube to the base.
A petrographic microscope is a type of optical microscope used in petrology and optical microscopes are derived from conventional brightfield microscopes of similar basic capabilities by: Petrographic microscopes are constructed with optical parts that do not add unwanted Download as PDF · Printable version.
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?
A petrographic microscope is a type of optical microscope used in petrology and optical mineralogy to identify rocks and minerals in thin sections.
Parts of the Microscope and Their Uses
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.
- Это совершенный квадрат. - Совершенный квадрат? - переспросил Джабба. - Ну и что с. Спустя несколько секунд Соши преобразовала на экране, казалось бы, произвольно набранные буквы.
Северная Дакота, - вслух произнесла она, пытаясь своим умом криптографа проникнуть в скрытый смысл этого имени. - Что говорится в его посланиях на имя Танкадо. - Понятия не имею. КОМИНТ засек лишь исходящую почту. В данный момент мы ничего не знаем про Северную Дакоту, кроме анонимного адреса.
Ненадолго, - буркнул Хейл. - Не зарекайся. - Я серьезно. Рано или поздно я отсюда смоюсь. - Я этого не переживу.
Да, подумал он, время еще. Он огляделся - кругом царил хаос. Наверху включились огнетушители.
Сьюзан не совсем понимала, к чему он клонит. Коммандер устало опустил глаза, затем поднял их вновь. - Сьюзан, выслушай меня, - сказал он, нежно ей улыбнувшись.
Вся моя жизнь - это любовь к моей стране. Вся моя жизнь - это работа здесь, в Агентстве национальной безопасности. Сьюзан слушала молча. - Как ты могла догадаться, - продолжал он, - вскоре я собираюсь выйти в отставку. Но я хотел уйти с высоко поднятой головой.
Беккер скорчил гримасу: что это за имя. Скорее кличка коровы, чем имя красавицы.
Халохот замедлил шаги. Мгновение спустя появились еще двое - тучный мужчина и рыжеволосая женщина. Они также подошли к Танкадо. - Неудачный выбор места, - прокомментировал Смит. - Халохот думал, что поблизости никого .
Единственное, что остается. Нужно было думать о долге - о стране и о чести. Стратмор полагал, что у него еще есть время.