54
Field diaphragm
The field diaphragm restricts the illumination light to
the area on the specimen to be observed. The field
diaphragm control on the right side of the microscope
changes the opening of the field diaphragm. Adjust the
opening of the diaphragm until it circumscribes the
field of view.
If a broader area than necessary is illuminated, stray
light may enter the optical system, creating flaring, and
reducing the contrast of the optical image.
In case of photomicrography, the setting of the field
diaphragm becomes very important. Generally, the field
diaphragm should be set to an area slightly larger than
the area to be exposed on film, that is, the photographed
area.
Perform the field diaphragm adjustment after
completing focusing and centering for the condenser
lens.
Aperture diaphragm
The aperture diaphragm controls the numerical aperture
of the illumination system, closely related to the
resolution of the optical image, contrast, and depth of
focus.
Rotating the aperture diaphragm ring (lever) on the
condenser for the diascopic illumination will change the
opening of the aperture diaphragm. Generally, the
aperture diaphragm should be adjusted to about 70 to
80% of the numerical aperture of the objective.
The scales for the condenser are provided as numerical
apertures. Check the value for adjustment.
Perform the field diaphragm adjustment after
completing focusing and centering the condenser lens.
Image of the
field diaphragm
Field of view of the eyepiece
70% to 80%
100%
70% to 80%
100%
Pupil of the objective
Aperture diaphragm
CUBE
A.S
.
EPI
DIA
EPI
DIA
Achr
N.A
0.9
0.2
0.3
0.4
0.5
0.6
0.7
0.8
=
Aperture
diaphragm
ring (lever)
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