There is a polarizer in the substage assembly, and a second polarizer called the analyzer between the objectives and the Bertrand lens. See section 2.3 for more information about how polarizers work. The polarizers in petrographic microscopes are plane (linearly) polarized. A vernier scale is constructed so that it is spaced at a constant fraction of the fixed main scale. For example, when line “1” on the vernier aligns perfectly with one of the lines on the ruler, then the distance is 5.1 mm. To determine a distance greater than 5.0 mm (but less than 6.0 mm), one identifies the line on the vernier which aligns with one of the lines on the main ruler. The distance starts at exactly 5.0 mm, when “0” on the vernier exactly aligns with “5” on the ruler. Figure 2.4.9 shows the distance reading recorded as the yellow vernier scale slides alongside the ruler scale. The vernier scale is a clever way of taking an accurate measurement reading between two markings on a linear scale by using mechanical interpolation. The rotating stage can therefore be used as a goniometer, or an instrument that measures rotational angle. The angle of rotation can be measured to the nearest tenth of a degree by using the markings on the vernier scale. The rotating stage has degrees marked on it: 360 degrees around the circular stage, in units of 1 degree. The rotating stage can be locked with the knob on the vernier. \)įigure 2.4.8.B.The rotating stage in action, showing how the angle of orientation can be measured using the goniometer and venier.
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