Olympus SC30 User Manual page 38

Appendix I: Microscope settings
Tungsten-halogen
lamps
Gas discharge lamp Gas discharge lamps stimulate gas at the atomic level using strong electrical
ND filter Many microscopes can insert ND filters into the light path, thus reducing the
Köhler Illumination
Condenser The condenser illuminates the sample. The main components are the aperture
Note
Principle of Köhler
Illumination
Tungsten-halogen lamps comply with their functionality to a conventional light-
bulb. Electricity flowing through a metal wire heats the wire to the extent that light
is produced (thermal emitter). In doing so, the wire emits a continuous spectrum,
hence a broad spectral band is emitted. One can control the brightness as well
as the color (color temperature) of the lamp by controlling the electrical current.
Tungsten-halogen lamps can be widely used in microscopy, especially when
acquiring color images.
fields. The excited atoms return to their initial state and, in doing so, give off the
energy which initially charged them in the form of electromagnetic radiation:
light. The resulting photons each have characteristic energy which is typical for
the gas being used. As a result, this type of lamp does not emit a broadband
spectrum like the halogen lamp, but instead emits discrete wavelengths. This
fundamental physical process cannot be externally influenced; hence, such a
lamp's perceived color is independent of the operation conditions. Because of
this discrete spectrum, gas discharge lamps do not emit a color-neutral illumi-
nation. Its adjustable high intensity light and the emission of short-wave spectral
bands required for fluorescent microscopy is an advantage.
intensity of the lamp's light. These ND filters ensure a uniform reduction of light
intensity throughout the entire frequency range without altering the color
temperature.
This illumination process which was described by Dr. August Köhler as early as
1893, is still an indispensable prerequisite for successful analysis using light
microscopy. The Köhler illumination enables an optimal, homogenous illumi-
nation of solely the part of the sample to be analyzed.
stop with which the size of the illuminated area is set and the condenser lens
which is responsible for the parallel emitted light rays. The condenser can be
opened and closed. The condenser is height-adjustable and horizontally
adjustable.
Adjust the aperture stop so that it coincides with the aperture of the objective in
use. Do not use the aperture stop to modify the light intensity. To do that, you
should always use ND filters or a lower lamp voltage.
You will find comprehensive descriptions of the principle of Köhler illumination in
microscopy text books. We will only give you a brief overview of some important
settings you should know.
Focussing the Field Diaphragm
One vital step when setting up the Köhler illumination is the sharp view of the
field diaphragm at the specimen level.
1)
Focus the object to be viewed.
2)
Close the field diaphragm so that only a small bright spot is visible in the
eyepiece.