Vignetting describes the effects by which the brightness of an image is reduced at its edge relative to its center. Vignetting of the input beam is generally caused by surface apertures. It may be intentional on the part of the designer in order to limit aberrations, or it may be an unintentional consequence of overfilling a system composed of optical components with fixed sizes.
The ‘Set Vignetting’ tool may then be used to determine the appropriate vignetting factors:
Vignetting factors are used to describe how the entrance pupil is seen by a field point in the presence of vignetting. These factors allow the shape of the input beam launched into OpticStudio to be modified to eliminate vignetting in the system. This is especially useful during optimization, when the use of vignetting factors may allow the more efficient Gaussian Quadrature sampling algorithm to be chosen.
Reference:
https://photographylife.com/what-is-vignetting
https://my.zemax.com/en-US/Knowledge-Base/kb-article/?ka=KA-01393
Zemax Optical Design Program User’s Guide, Zemax Development Corporation
