| 摘要 |
910,410. Exposure meters in reflex viewfinders AGFA A.G. March 9, 1959 [March 21, 1958], No. 8127/59. Class 98 (1). In a combined photo-electric exposure meter and reflex viewfinder for use with a photographic camera and comprising an optical system for producing an upright viewfinder image in combination with an objective and a reflex mirror, the photo-cell of the exposure meter is located behind a normally reflecting surface of the said system and either the said surface is rendered permanently partly light transmitting or means are provided for temporarily rendering the said surface partially or completely light transmitting. As shown (Fig. 1), where a pentagonal prism 5a in a viewfinder housing 8 a is arranged above a single lens reflex camera, the prism surface 9 is semi-silvered and has placed therebehind the photo-cell 10a of an exposure meter (not shown). In a first modification (Figs. 2-4, not shown) in which a ridged prism is used and a matt disc or matted lower surface of said prism optionally replaces the clear lens 4, both the surface 9 and a movable glass plate positioned between and parallel to surface 9 and cell 10a have alternate horizontal strips which are completely silvered or left clear, by which arrangement it is possible to present either a completely reflecting surface (when using the viewfinder) or a partially transmitting surface (when using the exposure meter). To facilitate the displacement of the glass plate, a frame member supporting said plate movable on two pin-and-slot guides is provided, spring detent means and a hand-knob being provided for locating said plate in either of its two operative positions. In a second modification (Figs. 5 and 6) provided with a ridged prism 5a, the photo-cell 10c is mounted behind a glass block 23, the angled surfaces 23a, 23b of which exactly fit the ridged surface of the prism 5c. The photo-cell and glass block are mounted in a frame 22 which is displaceable in the direction of the arrow A by pressing a knob 24 against the loading of a spring 27. When using the viewfinder, the block 23 is in its raised position (Fig. 5), but when it is desired to use the exposure meter, knob 24 is depressed, reflections at the ridged surface of the prism are destroyed, and light rays pass through to the photo-cell 10c. In further modifications, the prism is replaced by two plane mirrors, and the photocell is either placed behind one which is semisilvered (Fig. 7, not shown) or behind two glass plates, each of which has alternate silvered and plain strips for the purpose described above. |
