This paper introduces the testing of annular hyperboloid mirror with 460mm diameter in the Cassegrain system. To improve the testing efficiency and meet the requirements of utilization, the study is carried out from three stages: precision grinding, precision polishing, and optical coating. In the precision grinding stage, the annular Zernike polynomial is used to fit the measured surface combining with the data measured from the coordinate measuring machine, so that it can facilitate the testing of the distribution of the surface shape deviation over the entire surface. During the precision polishing stage, a feasible Offner compensator is designed to achieve the goal of high-precision testing of the hyperboloid surface, with a measurement accuracy of RMS≤0.02λ. Also, 0.5-0.7μm and 3-5μm dual-band high reflectivity and high uniformity reflective coating is designed for the Cassegrain system requirements, the actual test reflectivity is 96.2%, which can meet the design requirements.
Large aperture optical element deformed by its own weight is caused is one of the important considerations when we design the optical system, designing a mirror support solution that reduces the effects of gravity is critical. Traditional methods cannot effectively and intuitively analyze mirror distortion. In this paper, the finite element method and the optical surface fitting with Zernike polynomial are used to optimize the support scheme. These two methods are mutually verified and this method which use two parts is verified by the optimization scheme of the Φ900mm standard spherical mirror. With optimization, the steel belt loading and unloading weight hammer support scheme is finally adopted, and the best solution with Φ705mmin the circumference and each aperture is 55mm on the back of the mirror is obtained. The theoretical mirror surface’s PV and RMS value equal to 7.36nm (1/86λ) and 1.64nm (1/386λ), which is a good basis for guiding production.
With the development of the digital airborne photogrammetry technology, the more performances of the optical system for airborne mapping camera are required, such as the longer focal and the wider field of view (FOV). At the same time, the secondary spectrum correction becomes more important and difficult for the optical system design. A high performance optical system of airborne mapping camera with 200mm focus and 2ω=60° FOV is designed in this paper. The range of work wavelength is from 430nm to 885nm. A two-layer HDOE with negative dispersive characteristic is used to eliminate the secondary spectrum in the process of optical system design. The diffraction efficiency of the designed two-layer HDOE is up to 90%. From the result of design, the MTFs in whole fields are over 0.5 at 90lp/mm, which shows that the system has a great image quality. Meantime, the thermal analysis is done at the temperature range between -20°C and 40°C. As a result, MTF curves of the system at-20°C ~40°C show that a great image quality is kept, which meets the design requirements.
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