22
Fig. 26
Fig. 27
Fig. 28
Aperture Iris Diaphragm
· The aperture iris diaphragm determines the numerical aperture of the
illumination system. Matching the numerical aperture of the illumination
system with that of the objective provides better image resolution and
contrast, and also increases the depth of focus.
· Since the contrast of microscope specimens is ordinarily low, setting the
condenser aperture iris diaphragm to between 70% and 80% of the NA
of the objective in use is usually recommended. If necessary, adjust the
ratio by removing the eyepieces and looking into the eyepiece sleeve
while adjusting the aperture iris diaphragm lever
1
until the image shown
in Fig. 26 is seen. (Fig. 25)
2
Oblique Illumination (WI-OBCD)
(Figs. 27 & 28)
}The shading and 3D feeling of the specimen can be adjusted by varying
the width and orientation of the area subjected to oblique illumination.
This is possible with objectives from 5X to 100X.
# When the XLUMPlanFI20XW objective is used, oblique illumination
cannot provide a satisfactory effect due to the high NA (0.95) of the
objective.
The effect of oblique illumination assumes that the
field iris image is focused correctly.
Before proceeding to the following, pull out the ob-
lique iris insertion/removal knob
1
and bring the field
iris image in focus (this is the same operation as that
described on page 21).
1. Push in the oblique iris insertion/removal knob
1
.
2. Turn the knob
1
to adjust the width of the area illuminated by oblique
illumination. (Fig. 28)
3. Adjust the orientation of the oblique illumination by turning the top part
2
of the condenser.
}Pull out the oblique iris insertion/removal knob when using the condenser
as usual.
The width of the oblique illumination area is maintained even after the
insertion/removal knob
1
has been pulled out, so the same condition
can be reproduced the next time the knob is pushed in.
IMPORTANT
Aperture iris
diaphragm image
Objective pupil
70-80%
30-20%
1
2
