20~X Digital Zoom Optical System Design

A CCD is used as an image receiving device in the monitoring system which use the digital optical lens to image the target on CCD. The resolution capability of the lens directly determines the resolution cap ability of the whole monitoring system. A zoom lens has the advantages of not only finding the target in the large field of view but also identifying it in the small area. A long-distance-target monitoring zoom lens was designed in this paper in which the design method of the optical system and the design and optimization of the cam curve were descripted in detail.The domestic and foreign research results and development trends of zoom lens were introduced in chapter1. The basic concepts and the working principles of the zoom lens are descripted, the design met hods of the mechanically compensated zoom system are analysis and discussion in detail. According to the technical requirements, the structure parametersare determined by calculation with the help of typical zoom optical system selected.A zoom lens with focal length changes from17.5mm to350mm and the relative aperture changes from1/5.5to1/6.5are designed in chapter4. The entire lens is composed by17spherical lenses. Under the condition of good image quality, a movable aperture was used to minimize the total length and to improve the Vignetting in telephoto. Design requirements satisfied by the MTF curve is higher than0.3both on and off axial when spatial frequency is801p/mm. This zoom lens system has a continuously changed filed which cover the range of1°～20°, so it can search, track and detect a-long-distance target from field to filed continuously.The zoom lens system’s cam curve is studied in chapter5and the Gauss algorithm and fitting method of the curve are analyzed. The zoom curve and compensation curve were fitted by Matlab.