JPS55161221A - Photometric device - Google Patents

Abstract

PURPOSE: To make partial and full photometry selectable and neverthless enable the visual recognition of photometric range through the finder at the same time by disposing a liquid crystal plate which partially changes its transmittance to the focal plane of an objective lens or the plane near the same.

CONSTITUTION: This is so formed that the light from the taking objective lens is led to a focal plate 2 by a reflecting mirror 1 and the visual field image is obserbed through a condenser lens 4, pentagonal prism 5 and eyepiece 9. The photodetecting system is so constituted as to let the entire part of the focal plate 2 fall onto a photodetector 8 in an imaged or non-imaged state by disposing a small prism in the upper part of the pentagonal prism 5, making its interface as a semitransparent mirror and providing a photodetecting lens 7 right behind the same. The liquid crystal plate 3 which is disposed integrally with the focal plate 2 or in adjacency thereto lets the light of the entire part of the focal plate 2 enter the photometric system evenly in the state that it is not applied with electric field and therefore the unit is now in full photometry. If the liquid crystal plate 3 is so constituted that is causes a decrease in the transmittance of the shaded portion when applied with electric field, photometry may be done only by the light of the central part and it is also possible to visually recognize the range thereof through the finder system.

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