Most wide-field imaging lenses produce significant distortion.  The “Field Curv/Dist” analysis window quantifies the effect by plotting the percent difference between the landing position of the actual rays and corresponding reference locations.  The two most commonly used reference positions are calculated as: F-Tan(Theta) or F-Theta.  The first one corresponds to an ideal imaging lens with no distortion, while the second one provides the difference relative to a typical ideal scan lens in which the goal is to have F-Theta distortion (so the focused spot scans the image plane linearly with changes in the incoming field angle). 

You don’t need to worry about vignetting factors unless you have specifically set them to non-zero values.  If the vignetting factors are all zero (their default values), then checking or unchecking the box makes no difference.  In imaging systems in which apertures other than the stop clip rays, then vignetting factors can be used to modify the way rays are launched so as to avoid this clipping (and hence modify the way the pupil is filled).  You can read more in the corresponding help section.

You may also want to look at the Grid Distortion feature.  Here are results from the “Wide angle lens 100 degree field.zmx” example file:

Hey Ziv,

Vignetting factors are defined for each field point, whereas the distortion scan uses field as a continuous variable. OS will interpolate the VFs for an arbitrary ray using the two closest field points values. My preference is to turn them off, especially if you only have a few field points.

• Mark

That’s a great explanation Jeff! Indeed, the reason the feature is selectable is that the user does need to decide this. As a design matures, I like to shift all definitions to be ‘object sided’, remove VFs and use hard apertures instead, and increase the aperture slightly so the pupil is overfilled with rays. While this is wasteful in that you trace rays that don’t get through, it is physically realistic.

• M

Thanks a lot Jeff and Mark!

Your answers and explanations helped me to understand it better and also realize what OS does in order to decide which version to implement in different situations.

Ziv