Olympus BHT Buku Petunjuk - Halaman 14
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D.
Condenser Adjustment
,
1.
Condenser Centration
1)
Stop down the field iris diaphragm with
knurled ring
@
by rotating in the direc-
tion of the arrow. (Fig. 14)
2)
Use the condenser height adjustment
knob
@
to move the condenser up and
down until an image of the field dia-
phragm can be seen clearly in the eye-
pieces. The rotation of the knob in the
direction of the arrow lowers the con-
denser.
Field iris
diaphragm image
Field of view
- 7 g + ( ' J
Fig. 15
3)
Bring the field iris diaphragm image into the center of the field of view with the two con-
denser centering knobs
@.
(Fig. 14)
4)
Widen the diameter of the iris diaphragm progressively. If the polygonal image of the iris
diaphragm becomes inscribed in the field i t means that the field diaphragm i s centered.
(Fig. 15)
Field Iris Diaphragm
The field iris diaphragm controls the diameter of the ray bundle impining on the speci-
men surface and therefore, by stopping down the field diaphragm until i t is slightly
larger than the field of view, i t can reduce stray light, which in turn increases image defi-
nition and contrast.
In order to achieve optimum objective performance, the opening of the aperture iris
diaphragm should be matched to the numerical aperture of the objective in use. I t is
often preferable, however, to stop down the aperture diaphragm slightly more than in-
dicated by the objective N.A. This will result in better image contrast, increased depth of
focus and a flatter field.
After completing focus adjustment, re-
move one of the eyepieces from the ob-
servation tube and look into the empty
eyepiece tube. As you stop down the
aperture iris diaphragm, the image of the
iris diaphragm can be seen in the object-
ive pupil. Adjust the opening of the
diaphragm to match the N.A. of the ob-
jective in use. I f the specimen is low in
contrast, i t is recommended to stop down
to 70%
--
80% of the objective
N.A.
(Fig.
16)
Opening of the
aperture diaphragm
Objective exit pupil
I
Fig. 16