Measuring head for an apparatus measuring colour by diffuse reflection

Abstract

Abstract The light emerging from a lamp (1) infringes on the measuring object at 90 DEG . The light reflected from the latter is collected at 45 DEG by means of an annular mirror optic system (3-6) and is split up by means of two colour-selective interference mirrors (7, 8) into the three colours blue, red and green. The three colours then pass via further filters (9-11) and in each case one aplanatic lens (12) onto in each case one silicon-planar photodiode (13). In order to blank out light reflected directly from the surface of the measured object, two crossed linear polarisers (141a, 142a) are inserted into the beam path. In order to avoid difficulties with the interference mirrors (7, 8) which are sensitive to the polarisation direction of the light impinging on them, the linear polariser (142a) located in the imaging beam path is vapour-deposited on its rear with an lambda /4 layer (b) which brings about a circular polarisation of the light supplied to the mirrors (7, 8). <IMAGE>

Inventors

• 👤 Hans Ott

Bibliographic Details