Optical Design of a Reflecting Omnidirectional Vision System for Long-wavelength Infrared Light

A reflecting omnidirectional optical system with four spherical and aspherical mirrors, for use with long-wavelength infrared light (LWIR) for night surveillance, is proposed. It is designed to include a collecting pseudo-Cassegrain reflector and an imaging inverse pseudo-Cassegrain reflector, and the design process and performance analysis is reported in detail. The half-field of view (HFOV) and F-number of this optical system are 40-110 degrees and 1.56, respectively. To use the LWIR imaging, the size of the image must be similar to that of the microbolometer sensor for LWIR. As a result, the size of the image must be 5.9 mm x 5.9 mm if possible. The image size ratio for an HFOV range of 40 degrees to 110 degrees after optimizing the design is 48.86%. At a spatial frequency of 20 lp/mm when the HFOV is 110 degrees, the modulation transfer function (MTF) for LWIR is 0.381. Additionally, the cumulative probability of tolerance for the LWIR at a spatial frequency of 20 lp/mm is 99.75%. As a result of a thermalization analysis in the temperature range of -32 degrees C to +55 degrees C, we find that the secondary mirror of the inverse pseudo-Cassegrain reflector can function as a compensator, to alleviate MTF degradation with rising temperature.