A scanner for mechanically distinguishing light from dark areas of an image, having a light source 4, a collecting lens 7 directing light from the source to surface 11 of a total internal reflective block 62 (block 9 in FIG. 1). The top, parallel surface 13 reflects the light through a focusing, hemispherical...http://www.google.co.uk/patents/US4346292?utm_source=gb-gplus-sharePatent US4346292 - Coaxial optical scanner
