Distance

The choice of prescription specification is a little different from most other lens design and ray tracing programs. RayOpt associates with an element (surface):

• distance (or directional offset, measured in the global, unrotated coordinate system) of the element’s apex relative to the previous element’s apex.

• orientation (x-y-z Euler angles in the rotating frame) with respect to the directional offset

• element properties (type of element, curvature, aspheric and conic coefficients, focal length of an ideal element)

• optionally, the material after the element (behind the surface)

Ray data are given at (ray intercepts) or just after (direction cosines, paraxial slopes) the respective element unless stated otherwise (e.g. incidence angles).

The choice of associating the “distance to” and not the “thickness after” with a surface has several advantages: shifts, offsets, tolerances can be implemented in a more straight forward manner, ray propagation becomes more natural and efficient (transfer, intercept, refraction), ray data at the surfaces’ apex planes does not need to be tracked. The “thickness after” does not have much meaning in ray trace data as it can only be used later when tracing toward the next element and its direction is typically ill defined. Compared to most other programs the distance data is the thickness data shifted by one element towards the object.

Object and Image

Object and image are located at the first (index 0) and last (index -1) surface respectively. This naturally allows tracking their positions, material and shape data and supports curved objects and images naturally. Further data like pupils data are maintained in the two Conjugate s of the System.

Therefore, a minimal system of a single lens consists of fours surfaces: object, the two lens surfaces (one of which can be the aperture stop) and the image surface. The offset data of the first (object) surface does play a role in ray tracing but it can be useful as it locates the global coordinate system’s origin. The material of the last (image) surface is used as it can cause incident rays to be evanescent at the image surface. This can also be compared to other programs where the thickness of the image surface is never relevant or the material in object space and the position of the lens has to be tracked somewhere else depending on the implementation.