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Click Here For Best Selection Of High Quality Polarizing Microscope

Click Here For Best Selection Of High Quality Polarizing Microscope

In fitting up the petrographic polarizing light microscope, the instrument is first arranged as for use with parallel polarized light. The high power objective that is usually ¼ inch must be used. A system of converging lenses is fitted either beneath the stage or above the polarizer, and a lens called Bertrand Lens is placed in the tube of the polarizing microscope, either sliding in by means of a slot or fixed to the lower end of a drawtube. It is necessary to point out that some of these adjustments must be done with care, as the best results are not always obtained. Examiners should be quite sure that the nicols of the polarized light microscope are in used and are in crossed positions, that mirror or source of light is adjusted to give the best possible illumination, that the Bertrand Lens is in position, and that the converging lenses occupy their place between the polarizer and stage of the geological polarizing microscope.

 

            The effect may often be further improved by adjusting the objective and the converging system to the best advantage. The interference figure obtained in these circumstances with suitable sections of doubly refracting minerals is the best obtainable. But although the Bertrand Lens is a necessity if determinations of sign are to be made, it is not absolutely necessary in order to obtain a view of the figure.

 

            If all the adjustments here described, with the exception of the insertion of the Bertrand Lens, have been effected, the figure may be focused by means of an ordinary pocket lens held a little way that is usually between 1 in. and 3 in. above the eyepiece of the geological polarizing microscope. The figure may also be observed without the Bertrand lens if the eyepiece also is removed.

 

            It is sometimes useful to know the last two methods, because, although the figure obtained is not so large as that obtained with the Bertrand Lens, it is perhaps rather clearer. In the following description, however, it will be assumed that the lens is in use.



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Friday, February 15th, 2008 at 5:04 am
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Mineral characters Between Crossed Nicols in Convergent
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Click Here For Best Selection Of High Quality Polarizing Microscope