Optical–digital joint design of refractive telescope using chromatic priors

Jingang Zhang; Yunfeng Nie; Qiang Fu; Yifan Peng

doi:10.3788/COL201917.052201

Abstract

The conventional optical system design employs combinations of different lenses to combat aberrations, which usually leads to considerable volume and weight. In this Letter, a tailored design scheme that exploits state-of-the-art digital aberration correction algorithms in addition to traditional optics design is investigated. In particular, the proposed method is applied to the design of refractive telescopes by shifting the burden of correcting chromatic aberrations to software. By enforcing cross-channel information transfer in a post-processing step, the uncorrected chromatic aberrations are well-mitigated. Accordingly, a telescope of

F

-8, 1400 mm focal length, and 0.14° field of view is designed with only two lens elements. The image quality of the designed telescope is evaluated by comparing it to the equivalent designs with multiple lenses in a traditional optical design manner, which validates the effectiveness of our design scheme.

Telescope objectives are frequently applied in remote sensing, photography, and security surveillance applications. The performance of refracting telescopes is typically limited by chromatic aberrations that are inherently originated from the long focal length^[1]. In order to correct the induced chromatic aberrations, the most common methods are using cemented doublets or triplets that are composed of two or three optical materials with anomalous dispersion, such as ${CaF}_{2}$ and FK71^[2]. However, these carefully designed telescopes are usually expensive, troublesome to manufacture due to fragility, unstable in harsh environments, and unavailable in large apertures^[3]. McCarthy^[4] and Wynne^[5] proposed special optical layouts to eliminate longitudinal chromatic aberrations with normal glasses. Both systems consist of two or more widely spaced lens groups, which are not suitable for remote sensing and other narrow space occasions. Besides, these optical systems still suffer from lateral chromatic aberrations and other high-order monochromatic aberrations. Yang et al.^[6] introduced a four-group design, where most aberrations are carefully removed. Nevertheless, the design is still too long with easily more than seven components, increasing the manufacturing and assembly costs.