Optical design of an off-axis four-mirror objective system (OFOS) for a thermal camera

The optical design of a reflective objective system of a thermal camera for a syndromic surveillance system that captures bio-clinical signals, like temperature, directly related to the physical symptoms of the COVID-19 disease through thermal images is presented. The design is based on an off-axis four mirror system that allows for correcting spherical, coma, astigmatism, and field curvature aberrations. The OFOS design works on wavelengths of 7.5 μm - 14 μm, with an f-number less than 5, and a field of view (FOV) greater than 10 degrees.