Improvements in or relating to apparatus for a photometric comparison of lights of differing intensities

摘要

965,552. Photometric apparatus. C. REICHERT OPTISCHE WERKE A.G. Sept. 15, 1960 [Sept. 15, 1959], No. 31836/60. Heading G1P. A photometric device comprises means for directing light beams from two sources along two paths, means for combining the two beams, a transparent screen inserted into each of the two paths, the screens each having a pattern of non-transparent areas such that a non-transparent area on one screen corresponds to a transparent area on the other, the combined beam, as viewed, showing a pattern of intermingling dots, and an adjustable device in one beam to vary the intensity of that beam. As shown in Fig. 1, a cube 4 with a semireflecting interface 3 forms a virtual image of an illuminated pattern 5 on an illuminated pattern 4 so that the two patterns can be viewed through an eyepiece 8. In use, the mutual filter 9 is adjusted until the two patterns appear equally bright, the adjustment of the filter indicating the brightness of the light beam 6. In an alternative form, standard light 12 is incident on a rectangular reflecting strip 13 so that on a ground glass screen 15 two fields are visible, the one formed by the light 11 surrounding one formed by the light 12. Spaced from the ground glass screen 15 is a circular ground glass screen 17, the function of which is to blur the boundary between the two fields which are viewed through an eyepiece 14. The intensity of the standard light is adjustable by a neutral wedge 16.