Chapter 3 Usage of Components
34
3.3.3 Adjusting the Dia Field Diaphragm
Field diaphragm is intended to restrict the
observation range by changing the irradiation range
of the illumination. Adjust the field diaphragm using
the field diaphragm (F.S.) dial of the dia-illumination
section.
Operation:
Field diaphragm dial Field diaphragm
Turn it clockwise.
The diameter of the
diaphragm increases.
Turn it to the left.
The diameter of the
diaphragm decreases.
The field diaphragm has an index to indicate the
opening degree of the field diaphragm and the
following label.
F.S.
S.
F.
C
O
Controlling the field diaphragm
Tips on adjusting the field diaphragm
For normal use, stop down the aperture diaphragm until the illumination range is circumscribed by or
inscribed in the field of view.
An illumination range broader than necessary causes stray light to come in from other sources. As a result,
a flare occurs and the contrast of the optical image decreases.
Procedure for adjusting the field diaphragm
1. Place the objective with a specified
magnification into the optical path.
2. Turn the field diaphragm dial to stop down the
field diaphragm until the field diaphragm
image is seen in the field of view.
3. Turn the condenser focus knob to focus on
the field diaphragm image.
4. Turn the condenser centering screw to move
the field diaphragm image to the center of the
field of view.
Move the field diaphragm image to the center of the field
so that the image is about the same as for the field.
Adjusting the field diaphragm
Timing for adjusting the field diaphragm
Adjust the size of the field diaphragm each time the objective is switched.
Setting the field diaphragm when photographing using a camera
When photographing an optical image, a good result can be obtained by narrowing the field diaphragm to a
range a little broader than the size of the image sensor (frame indicating the shooting range).
Note that if the field diaphragm is narrowed close to the viewing range, vignetting may occur.
Field diaphragm
dial
Field diaphragm image
Field of view
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