ZEMAX Development Corporation thanks Dr. Ingolf  Hörsch of Sick AG for permission to use layout plots of the optical detector system used in this article.

Non-Sequential volume objects are 3D volumes which define some region of space. There are two major types of objects supported:

• Parametric objects, like the Standard Lens object. This is defined by parameters like front radius of curvature, back radius of curvature, center thickness and radial aperture. There are a wide range of parametric objects, including hologram, diffractive, cylindrical, biconic and more.
• Objects defined by data files. These include polygonal objects, tabulated faceted objects, and objects imported from CAD packages via STEP, IGES, SAT or STL formats. These objects may be facted, or have smooth continuous surfaces, or have regions of both faceted and continuous surfaces.

In either case, users need to place thin-film coatings and scattering functions on the surfaces of these objects to obtain the highest accuracy when simulating the propagation of light through them. ZEMAX uses the concept of a "face" to describe a region on the surface of an object to which a thin-film coating or scattering function is applied.

In parametric objects, the definition of a face is usually easy. For example, a standard lens is easily understood as having a front polished face, a rear polished face, and a rough, unpolished cylinder connecting the two polished faces.

When defining an object by a data file, defining a "face" may be more complex. Even a simple faceted mirror may be made up of many facets, which the human observer can clearly see make up a face, even though the mathematical description of that face may be very complex. When complex CAD objects are involved, we may be dealing with many megabytes of data, involving flat, curved, spline etc segments.

This article describes how faces are defined in general objects to help place coating and scattering functions on that object.