87
Focus the specimen. It may be easier to focus a
stained specimen first or the edge of the cover-
glass. Set Koehler illumination exactly (see
page 69), then find an empty area of the
specimen or remove the specimen.
Turn the polarizer (60.4) round the IC position
until the optimum extinction position is observed
through the eyepiece. This setting can be found
particularly accurately with a high-magnification
objective (40x or 63x):
Open the aperture diaphragm (48.21) as far as
the stop, engage the Bertrand lens (50.2) and
focus (50.3) or use the auxiliary telescope (Fig.
51) instead. The polarizers are exactly crossed
when the two branches of the hyperbola are as
near to each other as possible – or form a cross
(55a).
Fix this crossed position with clamp screws
(60.4 and 30.6).
Put the centering key (1.5) in the index
adjustment (60.5) and make the two index marks
(28.4) coincide; you will now be able to
reproduce the current polarizer setting later.
Adjustment of the condenser prisms
If the equipment was delivered together, the
condenser prisms will already have been
adjusted at the factory, but it is advisable to
check the adjustment from time to time,
especially after transport:
Disengage the objective side ICT prisms (60.7)
(pos. H).
Swing in the condenser top (48.15). Engage the
Bertrand lens (50.2) or use the auxiliary
telescope (Fig. 51).
Engage the condenser-side prisms (60.8) in
succession and focus the dark diagonal com-
pensation stripe. The whole-wave compensator
must be inactive, i.e. the engraving must be on
the side of the analyser that points downwards.
The dark stripe should be in the centre of the
brighter circular area. If not, proceed as follows:
push in the right-hand centering key on the back
of the condenser until it clicks into position and
rotate it until the stripe is in the centre of the
circle. The left-hand key is not required.
However, for the 3rd and 4th prism position
make sure that the left-hand centering screw for
the light rings is not rotated too far inwards or it
may obstruct the movement of the prism with
the right-hand key.
Ojectives for ICT
Transmitted light interference contrast is
possible with the brightfield and phase contrast
objectives which have the code letter of the
pupil position in the first line of engraving, e.g. A
and which are listed under the objectives
suitable for ICT on the optics data sheet.
Transmitted light interference contrast is also
possible with certain incident light objectives
(see separate objective table). A condenser
prism, e.g. K
1
must also be available for the
objective.
