2.2 Optical system selection and layout
There are three types of optical system structures: refractive, catadioptric, and reflective. Regarding the design of visible light/infrared dual-field imaging optical systems, Cassegrain catadioptric optical system and the total reflection optical system are mostly used in China. However, these two types of systems can only bear a small field of view angle. The infrared and visible light large field of view systems in this paper has a large view angle, so they are not considered. The refractive optical system has the advantages of a large field of view and high imaging quality. Therefore, the structure of the refractive optical system is adopted in this paper, and the plane mirror is appropriately used to fold the optical path and facilitate miniaturization.
The zooming methods of the optical system include axial movement zooming and cut-in and cut-out zooming. Since the cut-in and cut-out zooming method requires a large structural space, the axial movement zooming method is adopted. The cold diaphragm of the cooled infrared detector is set to eliminate the interference of stray light outside the field of view. The matching of the exit pupil and the cold diaphragm must be considered in the optical design to ensure 100% cold diaphragm efficiency, which is realized by directly using the cold diaphragm as the aperture diaphragm or placing the exit pupil of the optical system on the cold diaphragm while keeping its size consistent with the cold diaphragm. In addition, to avoid a too large aperture of optical parts at a long focus, the aperture of optical parts is compressed by means of secondary imaging, and a field diaphragm is set at the primary image plane to suppress stray light.
2.3 Optical system optimization scheme
The Gaussian optics theory is used to reasonably distribute the optical power. After calculating the initial structure, the optical design software Zemax is used to set the boundary conditions and optimize the initial structure. To make a compact optical system, both the infrared and the visible-light systems adopt the “positive-negative-positive” optical focal structure. The front fixed group and the rear fixed group are positive lens groups, and the zoom group is a negative lens group. In the optical path of the system, to reduce the volume, the infrared system uses three mirrors to fold the optical path, and the visible light system uses two mirrors to fold the optical path.
In order to facilitate the correction of off-axis aberrations and keep the size of the aperture diaphragm unchanged on large and small fields of view switching while considering the front and rear dimensions of the optical system, the aperture diaphragms of the infrared system and visible light system are placed near the middle of the optical path and before the rear fixing group. On-axis aberrations are corrected by using a lens near the position of the curved aperture stop, while the lens surface with a large light incidence angle is bent toward the stop to reduce advanced aberrations. In order to reduce the number of lenses in the infrared system and improve the transmittance and obtain satisfactory image quality, the infrared system introduces three high-order aspheric surfaces on the rear surface of lens 2, the front surface of lens 3, and the rear surface of lens 4 to balance on-axis spherical aberration and field curvature.
To ensure the material supply channel, the lens materials of the infrared system are commonly used single-crystal germanium, silicon, and zinc selenide, and the lens materials of the visible light system are selected from the materials with high frequency and excellent performance produced by Chengdu Guangming.
In this paper, a visible light/infrared dual-field imaging optical system for panoramic aerial reconnaissance cameras is designed, the detailed optical design indicators are given, and the structure of the designed optical system is analyzed. The visible light and infrared dual-field optical systems can be integrated by using the ground object scanning mirror and the spectroscope. The design results show that the imaging quality of the optical system is close to the diffraction limit, which can meet the practical needs of engineering.
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 HE F Y, CUI J C, FENG S L, et al.Narcissus analysis for cooled staring IR system[C]//Proceedings of the SPIE 6722, 3rd international symposium on advanced optical manufacturing and testing technologies: advanced optical manufacturing technologies.Chengdu: SPIE, 2007.
 Tang Tianjin, Li Yan. Common aperture dual-band imaging optical system for the infrared camera [J]. Applied Optics, 2015, 36(4): 513–518.
 Wang Ping, Zhang Guoyu, Gao Yujun, et al. Opto-mechanical design of visible and infrared dual-band aerial reconnaissance camera [J]. Chinese Journal of Mechanical Engineering, 2012, 48(14): 11–16.
 Bai Yu, Liao Zhiyuan, Liao Sheng, et al. Common aperture thermalized infrared dual-band optical system [J]. Optical Precision Engineering, 2016, 24(2): 268–277.
 Lin Zhaoheng, Tang Yong, Dong Ping, et al. Optical system design of variable magnification components of gun sights [J]. Journal of Electronic Measurement and Instrumentation, 2008, 22(S1): 207–211.
 Tian Tieyin, Wang Hong, Gu Fengan, et al. Optical system design of three-line array stereo mapping camera [J]. Optical Precision Engineering, 2009, 17(11): 2692–2698.
 POLLICA N J, ALEXEY C C.Wide-angle catadioptric optics for broadband applications[C]//Proceedings of the SPIE 8704, infrared technology and applications XXXIX.Baltimore, Maryland: SPIE, 2013.
 Zhang Huawei, Zhang Jinwang, Liu Xiujun, et al. Optical design of large relative aperture cooled infrared camera lens [J]. Infrared Technology, 2015, 37(2): 124–129.
 Gao Jinhong, Fu Yuegang, Liu Zhiying, et al. Design of 30× cooled medium-wave thermalized infrared zoom optical system [J]. Application of Optoelectronic Technology, 2013, 28(2): 13–17.
 Xu Lei. Optical system design and image quality evaluation of digital aerial cameras [J]. Optical Instruments, 2009, 31(4): 30–33.