Olympus POS Manuale di istruzioni - Pagina 10

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OBSERVATION METHODS

Standard

In principle, the polarizer, analyzer, test plate, and Bertram! lens should be slid out of the optical

path since they are not required for ordinary microscopic examinations.

In most cases, however,

the polarizer is left in the optical path.

II.

Orthoscopic Examination

Strictly speaking, in orthoscopic examinations, only light parallel to the optical axis of the micro-

scope enters the field of view.

In other words, only the parallel optical characteristics of the

specimen can be examined through orthoscopy.

Since, however, parallel light not only lacks

brightness but also weakens the resolving power of the lenses, weak aperture lighting is almost

always used by sliding the lower condenser lens into the optical path.

For ideal results, weak

aperture objectives as the 4x and lOx type should be used.

In this case, better results can be

obtained by adjusting the condenser iris to the aperture of the objectives.

The centering screw

can be used to rotate the specimen so that it will come in line with the center of the view field.

When the polarizer and analyser are clicked into position at 0°, the oscillation direction of each

coincides with the cross-line of the eyepiece—lengthwise for the polarizer and vvidthwise for

the analyzer.

This condition is called crossed Nicols.

When the analyzer is left out, the condition is called single Nicol or one Nicol.

By using both

methods, the following characteristics can be examined:

shape, size, and structure of the specimen,

refraction, double refraction, interference color, extinction angle, optical azimuth and optical poly-

chromism.

III.

Conoscopic Examination

In conoscopic examinations, optical phenomena are studied by throwing light from all directions

—with the exception of parallel light—on the specimen.

In other words, the specimen must be illuminated with circular beams.

Therefore, the numerical

aperture is increased by sliding the lower condenser lens out of the optical path;

furthermore,

large aperture 40x objective is used.

By inserting a Bertrand lens after focusing on the specimen,

an interference image, or conoscopic image, can be observed on the real focal plane of the objective

lens.

If a scaled eyepiece is used, the deflection of the interference fringe can be measured. The

interference image can also be observed directly through the tube without the aid of the Bertrand

lens and the objective lens.