Design and analysis of a fast aperture LWIR continuous zoom optical system

This paper presents the design of a continuous zoom optical system operating in the long-wave infrared spectrum (8 - 12μm), compatible with an uncooled detector having a resolution of 640×480 pixels and a pixel size of 12μm. Focal length ranges from 20mm to 100mm, with corresponding aperture values varying from F/0.8 to F/1.1. In order to possess good optical performance and compactness, the optical system applied a number of diffractive and aspheric surfaces. This system consists of 5 elements with a total length of 180mm and is optimized at 8 focal positions. All configurations exhibit good optical quality, with RMS spot sizes smaller than the sensor pixel size and MTF values at Nyquist frequency close to the diffraction limit. Additionally, in order to give the system good imaging performance in the operating temperature range from -20°C to 60°C, an active mechanical compensation method was used.