ZEMAX has several different types of apertures. First, there is a system aperture which defines the size of the beam travelling through the optics on axis. This aperture may be specified by the entrance pupil diameter, image space F/#, object space numerical aperture, or by the system stop size.

ZEMAX can trace rays which are launched either at the paraxial pupil, or at the real, aberrated pupil. This feature, known as ray-aiming, takes pupil aberration into account and  is absolutely essential in wide angle or fast optical systems.

Vignetting factors are also supported. These coefficients allow for pupil shrinkage and shift as a function of field.

There are also apertures which only allow a portion of the beam to pass. ZEMAX supports circular, annular, rectangular, elliptical, spider shaped apertures and completely user-defined. Obscurations are the complement to apertures, and they are also available in exactly the same forms.

ZEMAX accounts for the effects of apertures, obscurations, vignetting, and aberrated pupils in all computations.

 

The screenshot above shows the footprint of a beam of rays on a surface with a diagonal-shaped aperture. The aperture is  user-defined as a set of (x,y) points on the surface. Any number of apertures and obscurations can be applied to a surface or system.