Design of a two-mirror telescope using a free-form surface for the primary mirror

The design of a two-mirror telescope using a free-form surface for the primary mirror, to obtain a compensation of the spherical and coma aberrations, in the entire pupil of the telescope is proposed. In this design, the conic constant (𝑘1 ) of the primary mirror is a function of the heights, measure from the center to the edge of primary mirror. In this method, we use the exact ray tracing to find the optical path length (OPL) for each ray that intersect the primary mirror at different distances measured from the center of the primary mirror. The OPL is calculated with the sum of the distances that each ray travels until reaching the plane of the image, and the sum of the distances for a paraxial axial ray. From the optical path difference (OPD) of a set of rays, we obtain a set of values of the conic constant that guarantees that the OPD has a value of zero for each incident ray height. With the set of values of the conic constant it is possible to obtain the shape of the surface of the primary mirror.