VERY-WIDE-ANGLE OPTICAL-SYSTEMS SUITABLE FOR SPACEBORNE PHOTOMETRIC MEASUREMENTS

Spaceborne visible-light images for observing the large angular extent of the solar corona require 0.1% differential broadband photometry ov er similar to 1 degrees sky bins. When we are using a CCD camera, this specification requires spreading unresolved images over many pixels. Large images ease correction for aberration or field curvature. Permit ting large images allows simple and lightweight very-wide-angle design s employing spherical and toroidal mirrors and thick lenses that can v iew almost the entire sky. We present formulas and graphic results rel ating sky angle to focal-plane position and determining the tangential and sagittal focal surfaces governing image size at the CCD. Laborato ry measurements with two prototype configurations confirm the calculat ions. (C) 1998 Optical Society of America.