Chapter 3 Usage of Components
44
3.4.5 Adjusting the Diascopic Aperture Diaphragm
The aperture diaphragm adjusts the numerical
aperture of the illumination system. Adjust the
aperture diaphragm using the aperture diaphragm
open/close lever of the condenser.
Operation:
Aperture diaphragm
open/close lever
Aperture diaphragm
Turn it towards the right.
The diameter of the
diaphragm increases.
Turn it towards the left.
The diameter of the
diaphragm decreases.
To adjust the aperture diaphragm, observe the
pupil surface of the objective by using the
centering telescope. (See below.)
Display:
The following label can be seen on the aperture
diaphragm lever of the condenser turret
A.S.
Adjusting the aperture diaphragm of the condenser
turret
Adjusting the aperture diaphragm of the HNA
condenser slider
Relation between the aperture diaphragm size and the optical image state
Adjust the aperture diaphragm size to change the resolution, brightness, contrast and the depth of focus of
the microscope image.
The resolution and the brightness are decreased and the contrast and the depth of focus are increased by
narrowing the aperture diaphragm. They interact and cannot be adjusted individually. It is necessary to
adjust the aperture diaphragm size according to specimens to be observed and the purpose of the
observation.
Timing of aperture diaphragm adjustment and tips on adjustment
• Adjust the field diaphragm every time the objective is switched.
• Generally, images with an appropriate contrast can be obtained by narrowing the field aperture to 70%
to 80% of the numerical aperture of the objective.
Adjustment of the aperture diaphragm is important for BF microscopy, DIC microscopy, or image
photographing using a camera.
• When performing Ph or NAMC microscopy, fully open the aperture diaphragm. When the aperture
diaphragm is narrowed, the optical path is blocked.
Aperture diaphragm adjustment procedure
Adjust the aperture of the diaphragm while observing the
actual diaphragm image.
1. Place the centering telescope into the optical path.
2. Look through the centering telescope and turn the
eyepiece of the centering telescope to focus the
pupil (bright circle) of the objective onto the
aperture diaphragm image.
3. Adjust the aperture diaphragm so that the size of
the aperture diaphragm is 70% to 80% of the size of
the pupil of the objective.
70~80
100
Adjust the field diaphragm so that the size of the field
diaphragm image is 70
％
to 80
％
that of the pupil plane of
the objective.
Adjusting the aperture diaphragm
perture
diaphragm
open/close leve
erture dia
hra
m
Objective pupil
plane
perture diaphragm
open/close leve
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