Hyper-hemispheric and bifocal panoramic lenses

Abstract

Panoramic objectives are becoming, due to the availability of large area digital sensors, a diffuse optical system to catch very wide field of view (FoV). Typical panoramic lens have a view angle of 360° in azimuth (the plane orthogonal to the optical axis), just like a fish-eye, and plus and minus tens of degrees in elevation angle, i. e. above and below the horizon. Most common panoramic lenses use a curved, usually aspheric, mirror placed in front of a commercial objective to capture a 360° area around the horizon. More recent design use a catadiopter instead of a mirror. Both the solutions have the draw-back effect to obscure the frontal view of the objective, producing the classic "donut-shape" image in the focal plane. We present here a panoramic lens in which the frontal field is make available to be imaged in the focal plane, by means of a frontal optics, together with the panoramic field, producing a FoV of 360° in azimuth and 260° in elevation; it have then the capabilities of a fish eye plus those of a panoramic lens: we call it hyper-hemispheric lens. We design also a lens in which the frontal optics have a different paraxial focal length with respect to the equivalent panoramic; with this solution one can image, in the same sensor, the panoramic field plus an enlargement of a portion of it: that's the bifocal panoramic lens. Both the lenses have been designed and realized and we show here the optical scheme, the nominal performances and some pictures as an example.