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

Abstract

For conventional ultra-wide-angle or oblique cameras, it is difficult to fully correct the f − tan θ 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.

Realizing low-distortion in wide-angle lens with freeform optics technique

“…However, distortion is unavoidable because there is an extremely wide-angle lens. Xu et al reported a freeform-mirrorbased oblique imaging system with linear field of view 35°~65° and <1.1% distortion [6]. A point-by-point surface design method was applied to obtain the initial optical system, and then all the surfaces were converted to freeform surfaces during the optimization process.…”