Design of a linear field-of-view oblique imaging system with a low distortion

For conventional ultra-wide-angle or oblique cameras, it is difficult to fully correct the f-tanθ distortion without the scarification of the edge image performance. In this paper, we propose a linear field-of-view (FOV) oblique imaging system by varying the entrance pupil size over the FOV with freeform mirrors, and thus the diffraction limit around the edge field can be improved. An off-axis reflective system with conic surfaces has been selected as the initial system, and a point-by-point surface design method is then applied on the primary mirror to increase the entrance pupil size for edge fields in the FOV direction. All surfaces for the system converted to freeform during the optimization process, and the FOV of the final design can achieve +35^∘ to +65^∘, with a distortion less than 1.1%. It is possible to achieve a wide-linear FOV over 130° with a low distortion by the integration of two oblique systems and a central imaging channel.