Movie Makers (Jan-Dec 1952)

203 MAKE A REFLEX VIEWER For critical closeup work, this full-field optical unit is accurate and easy to use OWEN WILSON PARALLAX-CORRECTED viewfinders notwithstanding, there is in my judgment only one positive method of insuring accurate field of view in closeup filming. This is through the use of a reflex finder. The function of this important accessory, you will recall, is to project onto a suitable surface (generally ground-glass) an exact image of the scene which is scanned and will be recorded by the camera's taking lens in taking position. Such a finder is mighty handy for title shooting and, in fact, all other close camera work. And yet, without exhaustively checking on the matter, I'd say there are but two cameras today offering true reflex finders, with two others offering a similar service via an accessory. The built-in reflex cameras, of course, are the Cine-Kodak Special and the Pathe Super 16. Those offering a reflex finder function through an accessory are found among the magazine-type cameras made by the Bell & Howell and Eastman Kodak companies. Essentially in each case, the accessory is an optical system housed in a unit which may be inserted momentarily in the camera in place of the film magazine. . . . There was, of course, no such unit available for roll film cameras — so I decided to design a substitute. Its principal features follow. The overall outline of my reflex viewer will be seen in Fig. 1. Actually it is little more than a metal housing (or shell), with its outside dimensions determined by the design of the camera with which it is to be used. The key factor which determines these dimensions is the positioning of the viewer lens L, which in turn is determined by the position of the taking lens on your camera in relation to the camera s tripod socket. A specific example will make this determination clear. The roll film camera for which I designed this finder as you see it was a Cine-Kodak Model E (now no longer manufactured). On it, the center of the 1 inch lens was "HOI L^lo 51 ny o o * o — o H FIG. 2 FIG. 5 FIG. 4 BASIC DESIGN of the reflex viewer outlined by author is seen in Fig. 1 upper left. Unit is positioned momentarily on tripod in place of camera. 2% inches above the horizontal plane where the camera base met the tripod head. This lens center also was displaced by i/4 of an inch to the left of the center of the camera's tripod socket. Therefore, I positioned the viewer lens L on the front face of the frame by exactly similar dimensions in relation to the tripod hole H in the base B of the frame. This lens also should be about 3 inches ahead of the tripod mounting to create a correct angle of view. (Just for the record, my final overall dimensions of the finder housing were 4% inches in length, 2^4 inches in height and 1% inches in width.) For the finder lens L, any small lens of fairly good quality can be used; but it must be of the same focal length as the taking lens on the camera. In my case this was 1 inch, so that actually the optic I used was a projection lens from an 8mm. projector. For mounting, its barrel was soldered onto a metal plate V/$ inches square which was, in turn, centered and then riveted to the front of the finder frame (see Figs. 1 and 2). Behind this lens (in Fig. 1 ) is seen the movable groundglass screen S, about lx/8 inches square. The screen S is attached to the screen support by small clips CP, as will be seen in Figs. 1 and 3. This screen support is made of 1/32 inch sheet brass, forming a frame at the upright end and a horizontal slide at right angles which moves back and forth between the guides G (Figs. 1 and 3). At the inner end of the slide two vertical brass units are riveted so that they bear on the small brass cam C (Figs. 1 and 3) . When this cam is rotated by turning the knurled knob K (Fig. 2), the ground-glass screen is moved forward or backward to bring its image into focus, as seen on the mirror M through the magnifying lens L-2. The mirror M (Fig. 1) is held in place by a sheet metal bracket which is bent at right angles to permit it to be adjusted. The magnifying lens L-2 (which has a focal length of about 2% to 3 inches) is placed in a brass tube and soldered to a sheet-metal plate which is bolted to the top of the viewer. In arriving at their final positioning, you will find that some experimental adjusting must be carried out between the mirror M, the lens L-2 and the focusing plane of the screen S. With their relative positions determined, the screen and guides are mounted on a block of wood W and bolted to the inside of the viewer, as seen in Fig. 1. But before this mounting, the interior of the viewer should be painted a matte black, as should the inside of both lens barrels. The 1/32 inch sheet-metal bracket B (Fig. 1) is riveted to the front and back of the device to position the lens L in relation to the tripod socket exactly as is the movie camera lens. The tripod socket itself (H in Figs. 1 and 2) is drilled in the base of the bracket and tapped with a Y±/20 thread. Now, to assure that both the reflex viewer unit and the camera will be mounted on the tripod in exactly similar alignment, it is necessary to create some sort of pilot pin or reference guide on the tripod head. I did [Continued on page 216] CP at