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CINEiVTATOGRAPHIC ANNUAL
graphic lens to reach the camera aperture. The length of this opening is such that it corresponds to an angular opening of 230° of the regular disc shutter.
In the early days of Cinematography, the effects known as "fadein" and "fade-out' or "dissolves", which involve a gradual diminishing or increasing of the intensity of light which reaches the film, were obtained by gradually reducing or increasing the aperture of the diaphragm of the photographic lens. This system, although quite efficient, did not present sufficient guarantee of evenness of operation and presented some difficulties in obtaining the correct exposure for two different scenes which it was desired to "lap-dissolve" into each other when their illumination varied considerably.
The double disc shutter with automatic dissolve solved the problem very nicely. Both leaves of the shutter rotate at the same speed in the photographing of normal scenes, but through a control acces
Fig. 1 1 Main Sprocket and Crank Barrel. Bell 8 Howell Camera. A — 32 Tooth Main Sprocket. B— Train of Gears Operating Dissolve Mechanism. C — Oil Tube. D — Bevel Gear Driving Intermediate Shutter Barrel. E — Anti-reverse Dissolve Gear Mechanism. H — Magazine Take-up Belt Driving Groove. The 32 tooth film sprocket is solid with the crank shaft, so that for each revolution of the crank, 32 film perforations (8 picture frames) pass the sprocket. Train of gears B transmits mot:on to gears in the shutter dissolving barrel, which regulate the speed of the spiral shutter shaft and gradually open or close the shutter.
sible from the outside of the camera, one of the leaves can be made to rotate at an increased speed, and therefore while the camera is working at a constant speed the angular aperture of the shutter can be gradually reduced from its maximum aperture of 170° to zero or to any desired aperture between, or vice-versa — from zero to full opening or any desired aperture in a predetermined number of shutter revolutions.
The easily controllable variable aperture of the camera shutter is also useful for securing the correct exposure for each scene of a picture production without having recourse to variations in the opening of the lens diaphragm which involves alterations of the depth of focus of the lens and consequent unevenness in the photographic continuity of the photoplay.