Leica DMLB Bedienungsanleitung Seite 44

Operation of transmitted light darkfield
Watch the quality of the phase contrast image. If
using the auxiliary telescope, watch the image
with one eye through the eyepiece. Then repeat
the centration process for the other objective
light ring combinations.
CL/PH condenser (7.4; 7.7): Centration of the
light ring is not necessary.
Possible errors
Specimen: too thick, too thin, too brightly
stained; refractive index of mounting medium
and specimen identical so that there is no phase
jump.
Specimen slide too thick, so Koehler illumination
not possible.
Wedge-shaped coverglass
centration of light and phase ring is no longer
effective.
Wrong light ring, or light ring has been inserted
upside down (see assembly → p. 12). Aperture
diaphragm not open. Light ring not centered.
Wrong condenser top (UCA/P: 0.90 S1 only!).
Transmitted light darkfield with CL/PH and CLP/
PH, UCA/P condensers
Darkfield is possible with most objectives from
10x magnification; the image background may
be inhomogeneously illuminated at lower
magnifications.
44
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The highest possible objective aperture is 0.75,
although 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 identified 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 (Fig. 25.4).
Rotate the condenser disc (28.15) to position BF
or pull out DF light ring slide (7.7) as far as the
stop. Focus the specimen (10x objective). If you
have trouble finding the specimen plane,
temporarily close the aperture diaphragm
(28.14).
Set Koehler illumination (p. 37) (sharply focus
position, so
the centered field diaphragm together with the
specimen, Fig. 29).
Open the aperture diaphragm as far as the stop
(= PH pos.) and turn the disc to Pos. D (=
darkfield ring) or insert slide with DF light ring
into condenser CL/PH or CLP/PH (Fig. 7). If the
DF image is inhomogeneous with a homo-
geneous specimen, centre the DF light ring as
follows (does not apply for CL/PH and CLP/PH
condenser, Fig. 7.4): Use an objective with a high
magnification (40x – 100x), observe without an
eyepiece or insert auxiliary telescope (30.1) and
focus. Put the two centering keys into the
condenser (28.3) from the back at an angle and
adjust until the brighter circle (objective pupil) is
no longer asymmetrically illuminated. Optimize
image homogeneity by slightly adjusting the
height of the condenser.
Attention: