Optika Italy B-190 Serie Manuel D'utilisation page 15

9.8 Aperture diaphragm
• The Numerical Aperture (N.A.) value of the aperture dia-
phragm affects the image contrast. Increasing or reducing
this value one can vary resolution, contrast and depth of fo-
cus of the image. Move the diaphragm ring
value corresponding to the objective in use. In this case the
optimal setting of the condenser is achieved.
• With low contrast specimens set the numerical aperture to
about 70%-80% of the objective's N.A. If necessary, remove
on eyepiece and, looking into empty sleeve, adjust the con-
denser's diaphragm in order to obtain an image like the one
in Fig. 22.
9.9 Use of the polarizer (optional)
1. Remove the specimen from the stage.
2. Looking inside the eyepieces, rotate the polarizer until the
darkest position is achieved.
3. Once the dark is achieved ("extinction" or "Crossed Nicol"
position) it is possible to begin the observation.
(Fig. 21) on the
①
APERTURE
DIAPHRAGM
Page 15
①
FIELD OF VIEW
F ig. 21 F ig. 21
70-80%
30-20%
F ig. 22 F ig. 22