The Surface Module surface type is a construct which can be used to represent the behavior of an ideal lens by specification of a focal distance and image height mapping function. Keep in mind when using the Surface Module construct that the path lengths are only correct for the infinite conjugate condition. When path length accuracy is required, the Lens Module surface should be used. Polarized rays which are incident on a surface module will have their polarization state preserved in the absence of a polarizing coating.
The mapping function is a characteristic quality of the lens you are trying to model, but a "standard" lens will use the f-tan(q) function. In the first image below, an off-axis collimated ray bundle is input to a surface module at angle q. At the focal distance of the surface module, the image height of the ray bundle varies according to the mapping function as shown. The second image below graphs the dependence of image height on input angle for an incident plane wave and a surface module with a focal distance of 10 mm.
This feature can be accessed by selecting Surface Module (Perfect focus surface) as the surface Type on the Surface tab of a surface dialog box.
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