Leica DM R Serie Mode D'emploi page 70

Turning the condenser stop screw (48.13) or the
condenser height adjustment (48.12), lower the
condenser until the edge of the field diaphragm
is sharply focused (49b) and also centre the
image of the field diaphragm with the two
centering keys (48.16 or 27.1 and 27.5) (49c).
Open the field diaphragm (48.22) until it just
disappears from the field of view (49d). When
the objective is changed the condenser
centration may need slight correction. Adjust
the collector (48.19) until the image is
homogeneously illuminated.
Fig. 49 Koehler illumination
a Field diaphragm not focused, not centered, b Field
diaphragm focused but not centered, c Field diaphragm
focused and centered, but diameter too small, d Field
diaphragm diameter = object field diameter (Koehler
illumination)
a
c
70
The field diaphragm (48.22) protects the image
from unnecessary heat and keeps all light not
required for imaging away from the specimen so
that contrast can be enhanced. It is therefore
only opened far enough to just illuminate the
viewed or photographed object field. A change
of magnification thus always necessitates
adjustment of the field diaphragm.
b
d