Reflex system for cinematographic camera
BRIEF DESCRIPTION OF THE DRAWING 
     The above and other features of my invention will now be described in detail with reference to the accompanying drawing in which: 
     FIG. 1 is an axial sectional view of part of a cinematographic camera equipped with a reflex system according to my invention; 
     FIG. 2 is a front view of a light-reflecting shutter forming part of the system of FIG. 1, drawn to a smaller scale; 
     FIG. 3 is a fragmentary sectional view or a modified shutter body; and 
     FIG. 4 is a sectional view showing another shutter and light reflector according to the invention. 
    
    
     SPECIFIC DESCRIPTION 
     The camera shown in the drawing comprises an objective 1 (illustrated only in part) which is held in a mounting 16 centered on an optical axis 2. A film guide 4 in line with the objective adjoins the path of a motion-picture film F which is intermittently advanced by a non-illustrated transport mechanism, such as a claw drive, as is well known per se. A rotting shutter 3 on a shaft 17 is continuously driven, in timed relationship with the film transport, by a transmission including a gear 7 engaged by nonillustrated pinion on a motor shaft. 
     Shutter 3 has a sector-shaped body 6, extending here over an arc of 180°, which periodically obstructs the light gate 4 and carries a light-guiding body 8 of transparent material having substantially the same sectoral outline. Body 8, referred to hereinafter as a prism, has a flat front surface 12 transverse to the axis 2 and a generally dihedral rear surface with silvered and therefore internally reflecting frustoconical faces 9 and 10 meeting along an arcuate central ridge 18 which intersects the axis 2 throughout its rotation. Faces 9 and 10 have generatrices which include, like those of the adjoining lands of shutter body 6, an angle of 45° with axis 2. Thus, axially incident light rays A and B are reflected radially outwardly and inwardly toward respective lateral surfaces 13 and 11 forming the inner and outer peripheral boundaries of the prism; surface 13 confronts a photocell 5 with output leads 15 extending to a nonillustrated light indicator. The opposite lateral surface 11 of prism 8 is inwardly concave so that the radially reflected rays B are directed past the ridge 18 on their way to surface 13 and photocell 5. Slanting rays C striking the radially inner rear face 10 are reflected at lateral surface 11 toward front surface 12 at such a small angle that they will not leave the prism but are guided through the peripheral surface 13 toward photocell 5. 
     As shown in FIG. 3, a modified prism 8&#39; can have a body 6&#39; with a frustoconically rather than cylindrically curved lateral or peripheral surface 13&#39; at which axially incident and generally radially exiting rays A&#39; and B&#39; are forwardly refracted so as to allow a different positioning of the photoelectric sensor. 
     As illustrated in FIG. 4, a unitary body 106 of transparent material (e.g. a polyacrylate) with silvered rear surfaces 109, 110 can be used as a shutter 103 integral with a light reflector. Body 106 is shown mounted by a radial arm 106&#39; on a hub 106&#34; keyed to shaft 17. 
     End face, 14 (FIG. 2) of body 6, 6&#39; or 106 can be rendered opaque by a dull-black coating in order to prevent the escape of light rays at those locations. 
     It will thus be seen that virtually the entire beam of incident light traversing the objective 1 is redirected by the prism 8, 8&#39; or 106 toward a single sensor 5, the combined axial depth of that prism and the shutter being substantially less than that which would be required if the reflecting face 9 (or 109) were extended over the full radial height of light gate 4. 
     My invention is, of course, not limited to a rotary structure but can also be used with shutters reciprocating linerly or arcuately across a light gate.