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The Camera in Sound Pictures — Howell and Duhray 143
while the plane section comprises the camera aperture and the location of the registration fingers.
The central plane section of the film channel has been kept within the shortest possible length in order to insure perfect flatness of the film surface at the time of exposure.
The longitudinal curves impressed upon the film by the curved sections of the channel, in conjunction with the transverse guide and tension plates, prevent any possibility of the film sagging or curling even under very severe temperature conditions. The film is thus kept under control throughout its path in the channel and the presentation of a perfectly flat film surface at the focal plane of the photographic lens is thus assured.
The film channel consists of two members. The film is inserted in the space thus provided for and which is so designed as to provide a frictionless surface passage of the film through it.
A light spring pressure of the aperture plate against the body of the movement prevents possible injury to the film or to the mechanism, should the film be threaded improperly.
The aperture plate, is provided with a lock and the film cannot be introduced into the channel if the lock is not in its engaged position. This arrangement eliminates all possibilities of neglecting to lock the aperture when the mechanism is replaced in the camera after having been withdrawn from it for the purpose of cleaning even if this operation is performed under the greatest possible pressure of urgency.
A very light tension at one side of the film keeps it registered sidewise against a solid rail.
Figure 6 shows the arrangement of such tension which is exerted only on the portions of the film which assume the curved shape of the film channel.
The point on the floating tension plate at which the pressure is applied was determined by careful calculation, and is so located as to assure an equally distributed pressure along the entire side tension-producing surfaces.
THE FILM-FEEDING FINGERS : The function of the filmfeeding fingers, is to engage in the perforations, carry the film downward or upward, according if it is desired to record the motion of the subject normally or reversed, to withdraw from the perforations and resume its original position as at the beginning of the stroke.