GB1517468A - Cameras - Google Patents

Abstract

1517468 Camera viewfinders FRANKE & HEIDECKE GmbH [trading as ROLLEI-WERKE FRANKE & HEIDECKE ] 24 Aug 1976 [3 Nov 1975] 35160/76 HeadingG2J A viewfinder system for a reflex camera has a focusing screen which is formed as part of a liquid crystal cell. In Fig. 1 the viewfinder is shown as comprising two flat plates, 1, 2 of transparent glass or plastics material, spaced apart by a film 3, the space between them being filled by a nematic liquid crystal. The inner faces of the plates have transparent conductive layers 5 and 4, with respective current supply leads 7, 6. Layer 5 has at its centre a recess 5a, aligned with a micro-screen spot 9 on plate 1. Layer 5 is also interrupted along a ring 5b, so dividing it into electrically separate portions 5c, 5d, the portion 5d also having a separate supply lead 8. Different types of focusing screens may be produced merely by varying the voltages suitably on the different supply leads, without the necessity for having inter-changeable screens. Thus if a voltage is applied between leads 6 and 8, a local turbidity occurs in the liquid, so producing the effect of a frosted ring 5d. Such a screen is particularly suitable for photography in poor light. If there is zero voltage across leads 6 and 8, the screen is completely clear. In Fig. 7 (not shown) the microscreen area 9 is covered with a separate conductive layer having its own supply lead. In Figs. (not shown) 3-6, one plate of the crystal is formed by the plane face of a field lens or a Fresnel lens, and the other plate may be formed by one face of the viewfinder pentaprism. In Fig. 8 (not shown) one of the conductive layers is formed as a reflective surface. One plate may carry at one edge a number of electrodes 16, so shaped as to indicate diaphragm settings, so that a voltage between layer 4 and the appropriate electrode 16 will render the diaphragm setting visible in the viewfinder.