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 over ~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. Permitting large images allows simple and lightweight very-wide-angle designs employing spherical and toroidal mirrors and thick lenses that can view almost the entire sky. We present formulas and graphic results relating sky angle to focal-plane position and determining the tangential and sagittal focal surfaces governing image size at the CCD. Laboratory measurements with two prototype configurations confirm the calculations.