GB1191116A - Photographic Viewfinder - Google Patents

Abstract

1,191,116. Use of photochronism. VOIGTLANDER.A.G. 22 June, 1967 [25 June, 1966], No. 28815/67. Heading C4S. [Also in Division G2] A viewfinder for photographic purposes with an image-defining frame 5, 5a or 5b (see Figs. 1, 3 and 4, respectively) visible in the viewfinder image field consists of an objective comprising a layer of phototropic material 9 (see Fig. 1) or 11 (see Figs. 3 and 4), said layer lying outside the path of rays effective for illuminating the frame markings and which influences only the viewfinder image by its change in transparency. A Newtonian is shown in Fig. 1 comprising an objective lens 3, a phototropic layer 8, a partially reflecting mirror 4, eyepiece 2, an image defining frame 5 and a mirror 6. An Albada viewfinder is shown in Fig. 3 comprising a partially reflecting concave mirror 10, a phototropic layer 11, light conductors 12 with openings 14 framing opening 8, an image defining frame 5a formed as totally reflecting prism surfaces and an eyepiece 13. In a mod.fied Albada viewfinder shown in Fig. 4, the frame markings 5b are illuminated by a window 11 having a diffusion action. The frame markings 5b or the mark support are grained. The phototropic material may have a maximum transparency in its colour changing region of yellow-orange.