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Click Here For Best Selection Of High Quality Polarizing Microscope

Click Here For Best Selection Of High Quality Polarizing Microscope

The oculars or the eyepieces of the microscope are the lenses that slide into the upper end of the petrographic polarizing microscope tube. These oculars are used to magnify the image provided from the objective lens and it also focuses the light so that the human eye can accept it. Many microscopes come equipped with both high power as well as low power oculars. The usual magnification of oculars is between 5X and 12X. Multiplying the magnification of the ocular and the magnification of the objective lens used gives the total magnification of the microscope. The magnification will be increased by a high power ocular but the resolution will not change because the numerical aperture of the objective lens of the microscope controls the resolution. As much as an observer wishes to magnify the image of the object, it is highly possible. But then the amount of the details in the image viewed under the petrographic microscope does not increase or does not change at all. As the image is being magnified, the fuzziness is also magnified along with it. For practical purposes, about 1000 times the numerical aperture of the objective is considered as the maximum useful magnification to be used.

 

            Some oculars have markings like crosshair for instance. The upper part of the ocular lens is mounted for the purpose that it can be screwed in or out to bring the crosshair into a well-defined focus. Detents are also provided in the top of the microscope tube, which match a small peg on the side of the ocular. These detents allow the crosshairs to be accurately oriented N-S and E-W or in the 45 degree positions. Oculars are usually oriented N-S and E-W for routine work. On other microscopes like the binocular ones, only the right ocular is equipped with the crosshair or other markings.

 

            Some other oculars are known to be equipped with the micrometer scale. The main purpose of this is to allow the measurement of the size of grains on the microscope slide. The scale must be calibrated for each different objective lens by comparison with a stage micrometer. This micrometer is a microscope slide with millimeter scale on it that has been etched. The calibration is easily done by focusing on the stage micrometer and then by determining how many millimeters are represented by each unit on the ocular micrometer.

 

            There are also come conventional oculars that are designed for use without eyeglasses. In this type of oculars, the field of view through the microscope will be restricted if eyeglasses are worn. This is so because the eyes are kept too far from the oculars. If the eyeglasses are only worn to correct near- or farsightedness, the petrographic microscope can be used without the eyeglasses and the focus is only adjusted to compensate the problem. If the eyeglasses on the other hand are uses to correct some significant amount of astigmatism, they should be used in order to prevent eyestrain. Nowadays, many recent microscopes are equipped with high eye-point oculars. These are intended for use of eyeglasses and they are usually found with rubber eyecups that can be flipped up for use without eyeglasses.



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Wednesday, February 27th, 2008 at 3:42 am
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