Research on a 30 times ratio continuous zoom television optical system adjustment technology
Zhang Xiangming, Wang Zhongqiang, Chang Ming, Li Yuxi, Jiang Feng, Wang Zhangli, Ma Li, Zhao Wei     
Xi'an Institute of Applied Optics, Xi'an, Shaanxi 710065, China

Overview: This paper introduces a kind of continuous zoom TV. The zoom ratio reaches 30 times and the ratio of total optical length to focal length of small field of view reaches 0.5. The smaller the optical compression ratio of the continuous zoom system is, the higher the tolerance sensitivity of the system is and the greater the difficulty of mounting and adjusting is. The traditional debugging method is that the transmission optical axis of the former set of mirrors is taken as the reference, and the optical axis of the adjusting group, the compensating group and the rear group are coaxial with the former set of mirrors. However, the image quality is poor and it is difficult to meet the use requirements. Eccentricity error of lens and coaxial error of optical motion module are the main factors affecting the image quality of continuous zoom TV. The effects of eccentricity on the MTF (modulation transfer function) of the optical system were analyzed by optical software. The results show that the central error of the front mirror group is sensitive to the asymmetric aberration. Because of the existence of machining and alignment errors, the lens of the system produces translation and tilt relative to the optical axis, so the system produces asymmetric aberration. The front mirror group consists of three double convex lenses. If the convex sphere of the lens is well matched with the optical-mechanical interface of the high-precision diaphragm, the spherical center of the lower surface of the lens is automatically located on the central axis of the diaphragm under gravity. Adjusting the inclination of the lens will not affect the position of the spherical center of the lower surface, thus realizing the automatic centering of the lower surface of the lens. In this paper, the structural form of the spacer ring machine program is optimized, so that the lower surface of the lens is automatically centering. As the moving component of the system, both zoom lens group and compensation lens group are the key factors affecting the system image quality during the zooming process. In this paper, mechanical centering tooling is used to make the central axis of the moving assembly parallel to the axis of the guide rod. The optical axis of all components is corrected by the optical axis of the front mirror group. The optical system is precisely adjusted, and the optical resolution of the small field of view reaches 2.43″, which is close to the limit of diffraction resolution.