KERN Optics OBN 158, User Instructions

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OBN-13-BA-e-1510 16
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 OBN-13 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
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. If the microscopic image is
completely dark, the image for the field diaphragm is
outside the field of view and must be brought into the field
of view using the centring screws on the condenser.