Mitutoyo HM-200A Series - Adjusting Aperture Diaphragm

3. PREPARATION FOR THE TEST
No. 99MBG127A
3-5
3.2.2 Adjusting aperture diaphragm
The aperture diaphragm provided on the LED Illumination unit is for adjusting the
numerical aperture of the illumination. It affects the image resolving power, contrast, and
depth of focus.
Generally, the appropriate image contrast should be obtained by setting the numerical
aperture of the lens to be focused at approx. 80%.
Note that the resolving power may be lowered by excessively narrowing the aperture
diaphragm.
The numerical aperture at shipment is set to the maximum.
If required to change the numerical aperture,
· To lean the aperture diaphragm knob toward back side of the hardness testing
machine:
Numerical aperture --> Large, Image contrast --> Bad, Resolving power --> High,
Depth of focus --> Shallow
· To lean the aperture diaphragm knob toward front side of the hardness testing
machine:
Numerical aperture --> Small, Image contrast --> Good, Resolving power --> Low,
Depth of focus --> Deep
Fig. 3-6
Aperture
diaphragm
knob
Rear of the
testing machine
Front of the
testing machine
Contrast: Good
Resolving power: Low
Focal depth: Deep
Contrast: Bad
Resolving power: High
Focal depth: Shallow