Zuzi 137 Manual Del Usuario página 23

Regulate the height of the condenser to achieve a steady illumination of the field of view
(the more magnification the less field), in this way the regulation of the condenser will be
more accurate depending on the magnification: At 40x (objective 4x and eyepiece 10x) the
condenser will get down to cover a larger field and to avoid an intense illumination. The con-
denser will have to be raised progressively with the higher objectives to concentrate the light
beam and get a better illumination and contrast. With the immersion objective the condens-
er will have to be raised to its highest height.
The iris diaphragm allows to reduce the aperture to a similar value as the objective, and
in this way it can avoid a marginal illumination that decreases the contrast. Therefore it will
be closer when a low magnifying objective with small numerical aperture is used. In fact, the
total aperture will be only used with the immersion objective.
In order to carry out the adjustment you must start with the maximum aperture, as the
contrast increases because the diaphragm is closer, diffracting phenomenons appear which
limit the resolution. The correct adjustment will be obtained when we have the maximum
contrast without any change in the resolution.
An useful way of making the adjustment is the following
one:
Take away the eyepiece and observe the objective's exit
pupil through the empty tube, adjusting the diaphragm aper-
ture, generally it is convenient to keep the diaphragm apertu-
re about aprox. 70-80% of the objective numerical aperture.
(Pic.5)
The closing of the diaphragm, reducing the numerical aperture of the optical system,
increases the focal depth or penetration power. The diffraction limit can not be surpassed
under pretext of increasing the focal depth.
The diaphragm must not be used to reduce the intensity of the illumination.
Version 2 January-00 Instruction manual 50137XXX
Pupila de salida
del objetivo
70%-80%
30%-20%
Apertura del
diafragma Iris
Picture 5
Page 23