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Document 5: German Patent No. 309536, dated 28 July 1914

Device for the recording of sound-waves on film stock and such

Patented in the German Empire from 28 July 1914 onward.

It has already been suggested to use, for the recording of sound waves, several light beams in a triangular cross-section, which are moved crosswise to a mirror influenced by sound waves, behind which a light-sensitive film is passed.

The invention now concerns a particular device to produce these light beams and modify their number reflected from a mirror onto film. The invention proposes to achieve this by designing the reflective surface of the mirror that is steered by membranes so that the light beam reflected from the surface is split into several, for example, triangular light beams. This mirror can be arranged in such a manner that, for example, the mirroring surface at those spots where no light should be reflected is removed or covered with black matt paint, so that the mirror obtains a pointed form from the outset. This has the advantage over the arrangement of a pointed shutter between light source and mirror that there is practically no diffraction of light and thus the outline of the recorded curves is particularly sharp.

By moving a lens arranged between the light source and the mirror, the cross-section of the light beams reaching the mirror can be modified, so that one, two or more points or triangles are hit and a corresponding number of light beams is projected onto the shutter before the film band.

In the drawing (Illustration) the invention is presented with an example of application. Fig. 1 shows the overall device, Fig. 2 and 3 the mirror samples, and Fig. 4 the image band and the position of the light beams in relation to the image band.

From light source 1 a light beam 2 runs through the condenser 3, a bundling lens 4, a biconcave lens 5, and onto a mirror 6, from which it is reflected into shutter 7.

The shutter has a slit 8, which sits crosswise to the light-sensitive film band 9 that is being passed behind the shutter. The mirror 6 is attached to a frame, in which a membrane designed for the recording of sound waves is suspended, which is connected with the mirror through gate 12 so that the mirror must follow the oscillation of the membrane 11.

The light beam that falls onto mirror 6 is split into several beams (2.1., 2.2., 2.3) through the particular design of the mirror, which has either a pointed surface (Fig. 2) or contains several mirroring triangles (Fig. 3). These beams move crosswise to slit 8 in shutter 7 through the oscillation of the membrane. Thus, on the film band 9 a number of stripes 12 will be produced that corresponds to the number of light beams reaching the shutter, which will be of more or less width depending on the oscillation of the light beams.

By moving lens 5, the cross-section of the light beam reaching mirror 6 can be varied in such a manner that more or less points or triangles of the mirror will be reached and more or less light beams will be reflected onto shutter 7 and more or less stripes 12 will be produced on the film band so that a comfortable regulation of the sensitivity or accuracy of the registration is possible.

Patent claims:

1. A device for the registration of sound waves on film bands with the help of several light beams, which are steered with mirrors influenced by sound waves, which is characterised by the fact that the mirror has a mirroring surface that stands crosswise to the desired light beams (2.1, 2.2, 2.3) so that the light that falls on to the mirror is split only by reflection into separate light beams.
2. A device according to Claim 1, which is characterised by the fact that between the mirror (6) and the light source (1) a system of lenses (5) is arranged in such a way that by adjusting this system, a light beam of various cross-sections is cast onto the mirror and in it refracted into a smaller or larger number of mirroring subdivisions and a corresponding number of light beams is reflected on to the film band.

Illustration