76
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.
