Olympus BHT Buku Petunjuk - Halaman 14

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Condenser Adjustment

Condenser Centration

Stop down the field iris diaphragm with

knurled ring

by rotating in the direc-

tion of the arrow. (Fig. 14)

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

Bring the field iris diaphragm image into the center of the field of view with the two con-

denser centering knobs

(Fig. 14)

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

Fig. 16