Field of View vs. Resolution: Dual Field of View Optics
Optical systems for surveillance often employ a wide field of view for rapidly finding a target and another higher resolution, narrower field of view for target recognition and identification. A submarine periscope, for example, might employ a 1 1/2 x magnification and 32 degrees field of view for search tasks and a 6x magnification, 8 degree field of view for close up viewing.
The following pages describe some different optical approaches for achieving two fields of view. The Galilean telescope is employed in a reversed configuration for achieving a wide field of view by its placement in front of objective optics. A two-position field lens located internal to the imaging optics is presented as another means for achieving the dual field of view optics. In either case, emphasis is placed on controlling the entrance and exit pupil locations while satisfying the field of view and magnification requirements in order to preserve an unvignetted field of view.