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Figure 1-10. Frame Counting Mechanism.

b. Frame Counter (fig. 1-10). The frame counter advances one index each time the winding lever completes a stroke. An eccentric pin on top of gear D couples with a pawl. A spring-loaded, flat-headed pin on the under side of the pawl rides in an elliptical slot. The pawl engages a tooth of the frame counter ratchet gear as the eccentric pin rotates.

c. Rewind. After the film has been exposed it is on the take-up spool and must be rewound into the film magazine for removal. This is accomplished by setting the reverse lever to R , pulling up the rewind knob and turning in the direction of its arrow. Film, while being rewound, is properly tensioned by the take-up spool compensating friction clutch. The rewind knob is disengaged when it is pushed down. This assures smooth transport of the film while winding the shutter.

(1) Reverse lever. To rewind exposed film, the sprocket wheel must be disengaged from the winding mechanism so it will rotate freely. The reverse lever when placed in a horizontal position, depresses the coupling disc (fig. 1-2) of the sprocket wheel assembly. This disengages the sprocket wheel.

(2) Rewind knob assembly (fig. 21 and 31). The shaft (5) (fig. 31) of the rewind knob assembly has a gear on its lower end. This meshes with an intermediate gear on the bearing plate assembly, which in turn meshes with gear (6) of the rewind fork (7). The intermediate gear rotates the fork in the same direction as the rewind knob. The shaft (5) is held in its bearing by retaining screw (20) (fig. 21). When the rewind knob is pulled up, the key in its shaft engages forked carrier (24). A slotted friction sleeve fits over bearing plate assembly (3) (fig. 31) and rewind knob shaft (22) (fig. 21) fits over sleeve (23). A key, inside the rewind knob shaft, engages the slot in the friction sleeve. The friction of the sleeve prevents counter rotation of the rewind shaft while rewinding the film.

Figure I -11. Range-Viewfinder, Mechanical Schematic.

The components of the rangefinder and viewfinder are incorporated in one assembly. The magnification factor of the optical system is 0.7. The long base-length (68.5mm) of the rangefinder assures greater accuracy. The rangefinder, through a roller, couples to the focusing cam of the lens focusing mount. The viewfinder indicates the field of view of the 35mm, 50mm and 90mm lenses by bright-line frames which position automatically as the lenses are interchanged.

a. Rangefinder (fig. 1-12)

Figure 1-12. Range-Viewfinder, Optical Schematic.

Basically, the rangefinder is optical triangulization of fixed and movable images of the subject being photographed. The fixed image is the viewfinder image, and the movable image is controlled by a swinging objective lens. A cam on the camera lens focusing mount, through the rangefinder roller arm, transmits the focusing movements to the rangefinder objective lens (fig. 1-11). When the two images coincide, the lens is correctly focused.

(1) Optical system. Rays from the subject enter the fixed roof prism and are inverted. They pass through the objective lens, the mirror aperture, and an opening in the field lens, and are focused in the plane of the bright-line frames. An opening in the center of the metal mask permit formation of an aerial image. The image is viewed through the eyelens, and combines with the viewfinder image in the beam-splitting prism.

(2) Mechanical functioning (fig. 1-11, 26). As the lens focusing mount is rotated, a cam am on its rear surface, actuates the rangefinder roller arm. A cam on the upper part of the roller arm axel (23) fig. 26 moves the objective lever assembly through an arc. The swing of the objective lens changes the angle between the images. The objective lever assembly is spring loaded and mounted on ball bearing pivots (8).

6. Viewfinder (fig. 1-12). The viewfinder system consists of an eyelens, main prism with semi-transparent mirror, and a negative lens. A parallax-adjusting bright-line frame assembly outlines the field of various lenses. Disassociated optically, but coupled mechanically, is a frame selector (fig. 1-11) permitting preview of the fields covered by the 35mm, 50mm and 90mm lenses.

(1) Optical system (fig. 1-12).

(a) Subject viewing. The viewfinder, not considering the bright-line frame portion, has a simple optical system. Rays from the subject area enter a negative lens, pass through the beam-splitting prism and are imaged by the positive eye lens.

(b) Bright-line frames. The bright-line frame is imaged in the viewfinder by an optical system colligated for infinity. The optical components are an eye-lens, beam-splitting prism-lens combination, an achromatic lens, a field lens, a metal mirror with central aperture, and an illuminating window. Light, falling on the illuminating window, is directed by its prismatic surface to the mirror which is mounted at an angle. The mirror reflects the light to the bright-line frame assembly. The field lens, cemented on the glass plate, directs light to the smaller (90mm) bright-line frame. The achromatic lens, in combination with the lens surface of the beam-splitting prism, images the bright-line frame and directs it to the semi-transparent surface of the beam-splitter. The rays combine with the viewfinder image and are reflected to the eyelens.

(2) Mechanical functioning (fig. 1-11, 27).

(a) Bright-line frame assembly. The bright-line frames are contained between two cemented glass plates. The frame, corresponding to the lens mounted on the camera, is displayed in the viewfinder by the metal mask (7), fig. 27 which slides across the glass plate. The mask is actuated over a sliding bar (fig. 1-11), by one of the mounting lugs on the camera lens.

(b) Parallax compensation. Parallax is automatically adjusted as the lens is focused. The range-finder roller arm, when moved by the range sensing cam of the lens, also moves a wedged guide rivet which is attached to the roller arm axel. This moves the metal mask and glass plate diagonally across the field.

(c) Frame selector. Fields covered by the different focal length lenses may also be displayed in the viewfinder by operating a frame selector on the front of the camera. The frame selector moves a bar (fig. 1-11) which actuates a spring-loaded pin. The pin, through a slotted bar and lever arrangement, moves the metal mask across the glass plate. When the selector is pushed toward the camera lens the 90mm frame shows in the viewfinder, and when pushed away from the lens the 35mm frame is shown. The 50mm frame is positioned when the frame selector lever is in the vertical position.