Aperture Diaphragm; Use Of Oil Immersion Objective - Optika Italy B-510 Serie Manual De Instrucciones

9.9

Aperture diaphragm

• The Numerical Aperture (N.A.) value of the
aperture diaphragm affects the image contrast.
Increasing or reducing this value one can vary
resolution, contrast and depth of focus of the
image.
• With low contrast specimens set the numerical
aperture value ① (printed on the condenser ring)
to about 70%-80% of the objective's N.A. (Fig. 38)
If necessary, remove on eyepiece and, looking
into empty sleeve, adjust the condenser's ring in
order to obtain an image like the one in fig. 39.
Example: with objective PLAN 40x / 0,65 set the
scale to 0.65 x 0.8 = 0,52

9.10 Use of oil immersion objective

1. Focus the specimen with a low power objective.
2. Lower the stage (remembering to lock the coarse
upper limit lever).
3. Put a drop of oil (provided) on the area of the
specimen to be observed. (Fig. 40)
• Make sure that there are no oil bubbles. Air
bubbles in the oil damage the image quality.
• To check for bubbles: remove an eyepiece, fully
open the aperture diaphragm and observe the
objective exit pupil. (The pupil must be round and
bright).
• To remove the bubbles, gently move the nosepiece
to the right and left to move the immersion
objective a few times and allow the air bubbles
to move.
4. Insert immersion objective.
5. Return the stage to the upper focusing point and
obtain an optimal focus using the fine focus knob.
6. After use, gently remove the oil with a soft paper
towel or a lightly moistened optic paper with a
mixture of ethyl ether (70%) and absolute ethyl
alcohol (30%).
• The immersion oil, if not immediately cleaned,
could crystallize creating a glass-like layer. In
this situation the observation of the specimen
would be difficult if not impossible due to the
presence of an additional thickness on the
objective.
APERTURE
DIAPHRAGM
FIELD OF VIEW
Page 31
①
Fig. 38
70-80%
30-20%
Fig. 39
Fig. 40