In order to obtain a wider imaging field of view, freeform surface is used to design a large field of view space optical imaging system. The system uses an off-axis three-mirror optical structure with focal length of 1600 mm, F number of 8, and field of view angle of 20°×1°. Because of the large field of view, the image quality of general aspheric optimization design system cannot meet the requirements. In order to improve the freedom of system design, the Zernike polynomial freeform surface is applied to the tertiary mirror of the system, which enables the sagittal field of view to reach 20° further widening the imaging field of view. Degrees of freedom are increased effectively by the addition of the freeform surface. After optimization design, the optical transfer function of the system is better than 0.5 at 63 lp/mm, and the diffusion spot is optimized into Airy circle. The system energy concentration is high, and the imaging quality is close to the diffraction limitation.
Ultraviolet (UV) detection and imaging technology has developed rapidly in military applications due to its simple environment and clean background. Especially in the ultraviolet communication, UV alarm, UV detection and UV guidance has a unique advantage. A medium telephoto transmission type UV optical system was designed using optical software. This system consisting of two aspheric surfaces and one binary diffractive surface and the other 10 spherical surfaces is adopted to realize the long-wavelength infrared image design parameters: UV operating waveband of 240- 300nm, focal length of 200mm, field of view (FOV) of 24.8 degree, the F number of 2, and total length of 210mm. By optimizing materials and distributing power properly the system characteristics have been greatly improved. After optimization, the MTF is higher than 0.7 at the 20lp/mm and the maximum RMS radius is only about 10 μm, which is much smaller than pixel size of the detector whose pixel size is 13.5μm×13.5μm. The energy concentration in UV CCD receiving surface is greater than 82%. Under the premise that the system meets the UV warning and detection optical properties, the use of aspheric surfaces reduces aberrations, simplifies the structure. This system has high imaging quality and simple structure. In terms of warning, it has good concealment, small size and light weight advantages.
High resolution, wild field of view (FOV) and high image quality are required in space and airborne remote sensing and space photography. However, the refraction system must use special materials or complex structures to eliminate the secondary spectrum, the two-mirror system possesses limited degrees of freedom in correcting aberrations, and the coaxial system has serious central shielding problem in the case of wild FOV. According to geometry optical theory and primary aberration theory, an off-axis three-mirror (TMA)system with long focal length and wide FOV was designed based on the coaxial three-mirror systems. The spectral range is visible light range, the focal length is 5000mm, the FOV is 10°, and the relative aperture is 1:12. The primary mirror and the third mirror are aspheric surfaces while the second mirror is quadratic surface. In this system, the central shielding problem is solved and the modulation transform function (MTF) is more than 0.6 at Nyquist spatial frequency 50lp/mm which is close to the diffraction limitation. Moreover, the full field diffusion plaque is controlled into 5μm. In all, the analysis results show that the image quality and each specification of the off-axis three-mirror system satisfy the application requirements.