What's it about?
Freeform optical shapes or optical surfaces that are designed with non-symmetric features are gaining popularity with lens designers and optical system integrators. Manufacturing and testing details will be discussed for freeforms as well as current manufacturing tolerancing limits. This paper will address challenges that have been encountered in the manufacturing, testing, and handling of freeforms as their size expands up to and beyond 500 mm, and provide future work that will address each challenge.
The term “freeform” optic can be defined in many ways, but is usually characterized by a lack of rotational symmetry and a non-uniform radius of curvature. These qualities preclude the ability for the optic to be polished using conventional, full-aperture processes. Deviation from a best-fit sphere (BFS) is often used as a metric to describe the relative strangeness of a freeform surface. This paper will focus on large aperture (200 – 500 mm diameter) extreme freeform shapes. In this case, an “extreme” freeform is one which cannot be meaningfully fit to a BFS (possessing deviations from a BFS which are on the same order as the size of the part).