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# How Do I Change The Size and Shape of An Optical Component?

Question: Zemax OpticStudio draws all my optical surfaces as if they have circular apertures. How do I make it draw a rectangular cross-section, or some general cross-section?
Mark Nicholson
10/08/2015
OpticStudio

# How Do I Change the Size and Shape of an Optical Component?

Question: Zemax OpticStudio draws all my optical surfaces as if they have circular apertures. How do I make it draw a rectangular cross-section, or some general cross-section?

By default, Zemax OpticStudio assumes that all optical surfaces are of circular shape, and it computes the size of the circle by tracing marginal rays and setting the semi-diameter of the surface equal to the largest radial distance a marginal ray makes. (In non-sequential ray-tracing, the aperture of objects is defined as an object-specific set of parameters.)
This makes each surface just big enough to allow the marginal rays through. It is usually required to make the real lens larger than this: for example, the lens mount will need some glass to clamp against, and so the lens must be made larger than this semi-diameter. In some cases, the surface is in a caustic, and the marginal rays are not the limiting rays that should be used to define the component size. In other cases, it is required to make lenses with rectangular or other cross-sections. This is easy to achieve.

One way to make the lens larger than the circular aperture computed by Zemax OpticStudio, is to simply type the desired semi-diameter into the semi-diameter column in the Lens Data Editor. Alternatively, on the System Explorer, under Aperture, you can tell Zemax OpticStudio to add a margin either as a fixed amount in lens units, or as a percentage of the semi-diameter. This is particularly useful during optimization, as it ensures the lens is always large enough to be mounted.

To define other aperture shapes, expand the properties of the surface and go to the Aperture tab:

You may add circular, elliptical, rectangular, spider and user-defined apertures to the surface. It is usual, but not required, to use the same aperture shape on both sides of the component. For example, here is a cylindrical lens ground to have a rectangular aperture:

See the sample file Cylinger.zmx provided with Zemax OpticStudio in folder Samples\Sequential\Miscellaneous for a good example.

More complex apertures are easily defined using the user-defined aperture capability. All aperture types can be decentered for ease of placement.