Operation of transmitted light darkfield

Darkfield observation

Darkfield observation is not possible with condenser 0.30 S70, with condenser 0.53 S23 it is possible from 5x objective magnification, the max. usable objective aperture is 0.40. With condenser 0.90 S1, DF observation is possible from objective magnification 10x, the max. usable objective aperture is 0.75.

Objectives with higher apertures can be used if it is possible to reduce the aperture with a built- in iris diaphragm. These objectives can be recognised by the fact that the maximum and minimum apertures are given in the objective engraving and in our lists, e. g. 1.30 – 0.60.

Rotate the condenser disc to the H position (= brightfield). Focus the specimen (5x/10x objective). If the specimen plane is difficult to find, temporarily close the aperture diaphragm. Set Koehler illumination, open the aperture diaphragm as far as the stop (= pos. PH) and turn the disc to position D (= darkfield dia- phragm).

If the specimen does not appear against a dark background, centre the DF diaphragm with the centring keys. To do this, insert them in the openings in the disc on the left and right of the label plate for the DF diaphragm (D) (64.2) and rotate until a homogeneous dark specimen background is produced.

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Leica DM IRB manual Operation of transmitted light darkfield, Darkfield observation