<title>Design And Implementation Of A Continuous Zoom FLIR Optical System</title>

Abstract

Historically, FLIRs have usually utilized single-FOV or dual-FOV optical systems. The advantages of using a zoom optical system and thereby continuously varying the FOV coverage or scene magnification are numerous. Until recently, however, infrared zoom optical systems were considered to be impractical and incapable of providing acceptable image quality unless an excessive number of optical elements were used. A mechanically compensated, parallel-scan, 5:1 continuous zoom FLIR optical system has now been designed, debugged in the prototype stage, and is in production. Although the optical design was severely restricted by the packaging requirements, only six refractive elements are used, a number that is sufficient to ensure almost diffraction-limited image quality, especially toward the shorter focal lengths of the zoom range. Since two lens surfaces are convex paraboloids, special problems had to be solved to allow manufacture in production quantities. Thermal compensation, especially in the presence of temperature transients and gradients, was effected by using an analog computer to control the motion of one lens element in order to maintain focus.