VWR VisiScope TL384 POL Instruction Manual page 9

Numerical aperture setting
The value of the numerical aperture (N.A.) of the diaphragm is an indication of the contrast of the illumination
system. Matching the value of illumination system's N.A. with that of the objective ensures the best results in
terms of contrast and image quality.
To set the numerical aperture of the illuminator, adjust the opening of the iris diaphragm (4). In this way you con-
trol contrast and image resolution.
For samples with low contrast set the iris to about 75% of the value of the objective's numerical aperture.
HEIGHT ADJUSTMENT FOR
CONDENSER (5)
System centering
In order to correctly center the whole optical system, first remove the Bertrand lens out of the path by rotating its
disc. Remove also the lower polarizer filter.
The rotating stage is factory pre-centered and so it doesn't need any additional operation.
It's necessary to center the objectives following this procedure:
1. Place a specimen on the stage.
2. Insert 10x objective.
3. Insert the two little wrenches into the holes for nosepiece centering (7).
4. Focus your sample while continuously rotating the stage clockwise and then counter-clockwise by a little
angle (e.g. 30° or 45°). During these oscillations you should spot a point on the sample that doesn't rotate
on a circumference but only revolving about itself (fixed point). With the two objective's centering wrenches,
bring this point in the center of the crossline.
5. Insert the 20x objective.
6. Insert the two little wrenches into the holes for nosepiece centering (7), above the 20x objective.
7. Rotate the two wrenches until the same point of the sample is brought in the center of the crossline.
8. Repeat the operation for the other objectives.
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