Optimization Function Reference Points

Centroid The RMS or PTV computation of the data is referenced to the centroid of all the data coming from that field point. Centroid reference is generally preferred, especially for wavefront optimization. For wavefront optimization, reference to the centroid subtracts out the mean wavefront over the entire pupil, x-tilt, and y-tilt, none of which degrade image quality. Centroid reference also yields more meaningful results when coma is present, since coma shifts the image centroid away from the chief ray location. If the data is wavefront, the operand used is OPDX.

Chief The RMS or PTV computation of the data is referenced to the chief ray at the  primary wavelength. For wavefront optimization, reference to the chief ray subtracts out the mean wavefront over the entire pupil, but not x-tilt or y-tilt. Note the exact point at which the OPD is defined to be zero is arbitrary; this is the reason the chief ray reference subtracts out the mean wavefront. If the data is wavefront, the operand used is OPDM.

Unreferenced This option is only available if the data is wavefront. If the wavefront is unreferenced, then the OPD data with respect to the chief ray is used without subtracting the mean wavefront or tilt. If the data is wavefront, the operand used is OPDC.

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• Optimization Function Distortion and Color