Catadioptric lens for electrostatic copier - incorporates dichroic filter for blue light for better reproduction of blue matter on white background

摘要

A catadioptric lens system has the reflecting surfaces formed by one or more dichroic filter layes (14E) which may also be arranged that they reflect all light except that within a selected wavelength range. It is intended esp. for use in an electrostatic copying machine, to replace a blue filter, thereby enabling a differentiation between blue and white light to be made. The copier can thereby cope better with blue matter on a white background. The catadioptric lens (14) contains three separate lens elements (14A, B & C) as well as a flat element (14D). The surface nearest to lens (14 C has the layer(s) of filter material which selectively reflects some wavelengths and transmits others.