About
The aperture is assumed to be the only element of the system that limits the ray bundles. It is characterized by its position and its size. It can be located in object space, in image space or in an intermediate space.

The aperture location is selected in the Aperture position cell, which offers the following options:

- surface identifier - the aperture is located on a surface of the system,
- telecentric in the object space - the aperture is at infinity in object space,
- telecentric in the image space - the aperture is at infinity in image space.


The aperture size can be defined in several ways, selected in the type column:

- Object NA - numerical aperture in object space,
- Image F/# - working paraxial F-number,
- Aperture diameter - diameter on the surface designated as the aperture,
- Half angle - half aperture angle in object space.


The aperture can be shifted laterally, i.e. its center can be offset from the center of the surface designated as the aperture (if any), or from the Z axis of the coordinate system of the corresponding space when the aperture is telecentric.

Shifts are defined either as angles for telecentric systems, or as decenters when the aperture is defined by a surface of the system (respectively the angle and decenter choices in the center shift cell).

For systems telecentric in object space, X shift and Y shift are the angles of the chief ray with respect to the "X" and "Y" axes of the object surface coordinate system.
For systems telecentric in image space, they are the angles of the chief ray with respect to the "X" and "Y" axes of the coordinate system of the surface immediately preceding the observation surface.
When the aperture is defined by a surface of the system, X shift and Y shift are the "X" and "Y" coordinates of the aperture center in the coordinate system of that surface.