Incident Light Darkfield - Leica DM R Serie Mode D'emploi

Engage the Bertrand lens (50.2) and focus (50.3)
or remove an eyepiece and look into the tube
from a distance of a few centimetres. Mount the
centering keys (23.8) and adjust so that the
closed diaphragm lies in the centre of the
brighter circle (= objective pupil). Open the
aperture diaphragm until it is just visible in the
brighter circle (=
illumination aperture is then equal to the
observation aperture.
After returning to the normal observation mode
(Bertrand lens disengaged) image contrast can
be individually adjusted.
If the aperture diaphragm is stopped down too
far – especially at low and medium objective
magnifications – the object structures will
exhibit pronounced diffraction phenomena.
The aperture diaphragm can be stopped down
further for high-power objectives to improve
contrast and depth of field. Fine-adjust the
aperture diaphragm, watching the structure and
topography of the object, to obtain the best
contrast and resolution.
98
objective pupil).

Incident light darkfield

Special darkfield objectives (BD, Fig. 40) with
built-in annular mirror or annular lenses are
required for incident light darkfield. These
objectives have a greater external diameter and
screw thread M32 x 0.75.
High light intensity is necessary for darkfield, as
The
this type of illumination is produced by diffracted
and scattered light. Therefore, remove all filters,
polarizers, IC prisms, etc. from the light path and
set maximum intensity.
Make sure the front lens of the objective is
clean as this has a great influence on the
imaging quality in darkfield.
Pull out the incident light diaphragm module
HC RF (65.9) as far as the first (= channel 2) stop.
The aperture and field diaphragm functions are
then set.
A neutral density filter (65.10) can be engaged in
the light path to adjust the image intensity when
switching to brightfield.
This neutral density filter is only in channel I. It
saves the user from having to reduce the lamp
intensity and is particularly useful when
switching quickly between techniques DF ↔ HF.
Oblique light
For brightfield illumination the illuminating cone
is rotation-symmetrical to the optical axis. For
oblique light the aperture diaphragm (65.11 and
65.12, for channel I only) is moved to the side and
stop p ed down so that the illuminating cone hits
the sample at an angle, highlighting the surface
topography.