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127Appendix
6.3.2
Minimal Beam and Pupil Diameter
The detection of higher order wavefront terms up to a certain Zernike order requires
a minimum number of detected microlens spots. The minimum number of spots must
equal or exceed the number of Zernike modes to be calculated. See chapter Zernike
Fit and Zernike Modes .
Consequently, this minimum number of spots requires a beam and pupil diameter of
minimal size. The following graph shows the dependency for both available
microlens arrays of 150 and 300 µm pitch.
For a desired Zernike order you need to set the pupil to the required diameter within
the Pupil Definitions Setup . Also your physical beam diameter needs to illuminate
at least the same camera area so that the required number of spots can be
detected.
In case of unfavorable pupil settings, warnings or errors may occur. See chapter
Measurement Warnings and Errors for a detailed description and suited
arrangements for its prevention.
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