Improvements in or relating to apparatus to focus light on a surface

摘要

Focus control apparatus in which a focusing means of appreciable chromatic aberration is used (eg a zone plate). Focusing is achieved by varying the wavelength of light falling on the focusing means. This is achieved in three ways i) actually varying the light source ii) using a prism (16, Fig. 1) to pick out certain wavelengths iii) using an interference wedge. Application in video recorders and endoscopes mentioned.