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Using the Geometrical OTF vs Spatial Frequency plot

The OTF vs Spatial Frequency plot is a plot of contrast versus spatial frequency, for specified fields and waves. The calculation is geometrical.

To create the plot window:

  1. Select from the menu Analysis > OTF > Geometrical > vs Spatial Frequency

mtf snaphot

The OTF is displayed as a function of the spatial frequency. Both a tangential and a sagittal scan is made, with the sagittal scan plotted as a dashed curve.

Options panel

Field
Using the Field popup menu, select the field for which you wish to calculate. Select All to calculate for all fields (this can be time-consuming).
Wave
Using the Wave popup menu, select the wave for which you wish to calculate or Polychromatic, in which case a weighted average of the waves is calculated, using the weights specified in the Sources dialog.
Number of rays
This is the number of rays used to sample the pupil. The number of spatial frequencies is fixed at 20.
Use hybrid form
Multiply the calculated geometrical OTF by the diffraction limit, to give a curve that always lies below the diffraction limit.
Plot diffraction limit
Plot the diffraction limit. n.b., assumes Fraunhofer diffraction.
Divide by focal length
Divide the image space spatial frequency (cycles per unit length) by the focal length of the lens, so that it becomes an angular frequency (cycles per unit angle).
Plot real and imaginary parts
In addition to plotting the MTF, which is the absolute value of the complex-valued OTF, also plot the real and imaginary parts of the OTF.
Spatial freq.
The spatial frequency at which to calculate the OTF and MTF.

See also