A design study of dual-field-of-view imaging systems for the 3–5 µm waveband utilizing focal-plane arrays

In this work, a design study of switchable dual-field-of-view (FOV) optical systems for 3– 5 µm imaging using infra-red focal-plane arrays is presented. In order to switch the FOV, two different optical configurations are explored and compared for their merits and demerits. The first scheme is based on the axial motion of a lens group and the second is based on a rotate-in motion of two widely separated lens groups. It is found that the rotate-in scheme achieves better optical performance in both narrow-and wide-FOV modes due to its improved colour correction. Moreover, this scheme can achieve very wide FOV (up to 90° full diagonal coverage) with good optical performance using fewer lenses. Diffractive and aspheric surfaces are utilized to control colour and monochromatic aberrations, reducing the total lens count. The final optical designs along with their aberration curves and polychromatic modulation transfer function plots are presented, showing excellent performance in both FOVs.