KERN Optics OBD 127, User Instructions, Page: 24 / 27

23 OBD-1-BA-e-1510
Simple phase-contrast unit
This consists of a simple PH condenser, a PH objective with a specific magnification
(10x, 20x, 40x or 100x), a PH slider, which is adapted to the lens being used, a
centring telescope and two green filters.
To use this, you need to replace the standard condenser of the microscope with the
PH condenser. One of the objectives in the nosepiece is also replaced with the PH
objective and this is positioned in the beam path.
With the surface marked “TOP” facing up, the PH slider is pushed upwards into the
insertion point on the PH condenser until it clicks into the first position. At this first
position, the phase ring of the PH slider is in the beam path. If the aperture setting on
the PH condenser is set to “PH”, then the phase-contrast application can begin. In
order to return to the bright field application, you must push the PH slider further to
the second click position. At this point there is no PH ring as in position 1; the beam
can pass without being affected by the PH slider.
The PH objective has a PH ring in its lens system, just like the PH slider. Due to their
size on one hand and their positioning on the other, these two rings must be aligned
to one another in the beam path. The position of the ring in the objective cannot be
altered, that of the ring in the slider however can be. Although it has been pre-
centred, it may still be necessary that after a certain period of use it will need to be
re-centred using the three Allen bolts on the side of the slider and the centring
telescope (
see illustration ) .
When installing the centring telescope instead of one of the eyepieces there is
appearing an image of a white (slide) and a black (objective) ring in the field of view.
The black one is located centrally and the white one possibly shifted to the side (
see
left illustration ). Now the position of the white ring has to be adjusted in order to effect
an exact overlapping of both rings ( see right illustration ).
Depending on the preferences of the user, using a green filter can produce a more
effective and pleasant image. To achieve this, the green filter must be screwed onto
the underside of the PH condenser.