Compact design of a continuous zoom in the MWIR with a HD detector

There is a growing interest in infrared technology for surveillance, military and space applications. Designs in infrared waveband have evolved taking advantage of new detector developments. New generation of High-Definition detectors allow for better performance and resolution. The increase in image field height, implies new challenges for designers to achieve aberration correction and unwanted light control. The need to use different fields of view and a rapid response to switch between different FOVs, increases the interest for continuous zoom in infrared. In such systems it is a significant challenge to control the parameters previously mentioned for all zoom positions. This paper presents a compact 10:1 optical zoom, with focal lengths from 20 to 200mm, F#2.8 in the 3.6-4.2µm waveband, with a 1280x1024 pixels, pixel pitch 7.5 µm cooled detector. The design consists in seven lenses. The optical system is able to focus at 25m near distance for SNFOV and 10m for WFOV. Athermalization ranging from -40ºC to 70ºC is achieved with an active focusing lens system.