Description

Lenses, Mirrors and Prisms are special constructs in FRED and each carries a special set of properties which define their existence.  As such, the following rules apply and must be respected.

Application Notes

Closed solids and removing surfaces

Lenses, Mirrors and Prisms are closed solids. As a result, individual surfaces cannot be removed.

Surface axis of symmetry

The individual surfaces which make up Lenses and Mirrors must share a common axis of symmetry.  Therefore, one optical surface of a Lens cannot be tilted with respect to the other surface unless the element is first converted to a Custom Element.  In the example below, the lens on the left obeys the axis of symmetry rule while the lens on the right does not.  The lens element on the right is a custom element.

Material immersion

Lenses, Mirrors and Prisms must be immersed in a common material. Therefore, no surface of a Lens, Mirror or Prism can be in contact with another element or material except under the following conditions:

•the individual optical elements are converted to Custom Elements

•the "Glue" feature is invoked to cement the contacted surfaces. Note that there must still be a non-zero spacing between the surfaces when a glue layer is used.