KERN OBL 145, User Instructions

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15 OBL-14-15-BA-e-1610
5.6 Adjusting the Koehler illumination
To make sure that perfect image results are achieved during microscopic
observation, it is important that the direction of light of the microscope is optimised. If,
as with the devices in the KERN OBL-14 and OBL-15 series, the lighting can be set
in accordance with Koehler, the result is homogenous illumination of the slide and
avoidance of disruptive stray light.
The necessary control elements for this are:

Height-adjustable and centre-adjustable condenser with aperture diaphragm

Field diaphragm
Note: The condenser of the microscopes of the series OBL-14 and OBL-15 is not
centre-adjustable. Therefore it is not a full Koehler illumination. However this is
regarded as Fixed-Koehler, since the condenser is pre-centred.
When adjusting the Koehler lighting for the first time, you must first select the lowest
possible objective magnification, so that you can carry out the following steps.
1. Use the condenser focus wheel to position the condenser
directly below the specimen stage. Switch on the lighting
and use the coarse and fine adjustment knob to bring the
slide with the cover glass positioned facing upwards into
focus.
2. Close the field diaphragm completely using its adjusting
ring. When you look in the microscope a blurred image
appears in the aperture.
3. Adjust the height of the condenser until the image from the
field diaphragm appears clearly in the field of view. For
some microscopes there is a risk that you will lift the
condenser up so high that it collides with the object holder.
Therefore care is needed when doing this.