No. 99MBA091A
3-4
When measuring cylindrical workpieces or screw threads, the numerical aperture affects
measurement accuracy. The appropriate optical aperture is shown as below:
（１）
For cylindrical measurement
Aperture D＝0.18F F；Focal distance of condenser lens (mm)
＝19.224
（２） For screw thread measurement
Aperture D＝19.224
D
：
Corresponds to the aperture setting 1 to 25 indicated on the aperture diaphragm
knob on the control panel of the measuring unit.
d
：
Workpiece diameter
d2
：
Pitch diameter of screw thread
α
：
Screw thread angle
The following graph shows the correlation between the workpiece diameter d and the optimal
aperture setting D. Adjust the aperture diaphragm knob to the optimal position by referring to
this graph.
1
d
3
1
d
3
sin
d2
3
α
2
Workpiece diameter d (mm)
Aperture D (mm)
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