The present invention relates to processes for transcribing a video disk onto a cine film. The term video disk, which is now in standard use, is used to describe disks carrying the recording of television signals.
Such disks and apparatus permitting the recording and reading thereof, generally optically, are known. The most widely used method consists of recording television signals, suitably coded in the form of a series of lines of variable length and spacing distributed along a spiral path centered on the centre of the disk. To read the disk, the reading head is moved radially by a lead screw for example. This reading head comprises an optical device permitting the illumination of the path and the collection of the changes in the light beam made by the inscribed lines. As the path is very narrow and the spiral very tight (of the order of a few microns) this optical device generally has tracking servomechanisms, permitting, for example by means of an oscillating mirror, the tracking of the path in spite of the irregularities of varying magnitude and types, such as the eccentricity of the disk and irregularities of the lead screw.
In conventional manner, two fields, corresponding to a single frame, are recorded for each rotation of the disk and this fixes the rotation speed of the said disk, because the duration of one frame is standardized and must be respected in order to be able to provide a television set with the appropriately decoded reading signals. The motor which radially drives the reading head is controlled by the mean value of the error voltage of the tracking servomechanism. Thus, on normally reading the disk, the head advances at the average speed of one path per revolution. If, however, an acceleration or deceleration is required, a pulse is applied to the tracking servomechanism in order to jump a turn, forwards or backwards depending on the particular case, at the end of a frame. This changes the average value of the error voltage and the radial advance motor is automatically adjusted to the necessary speed. On systematically rereading the same frame, the motor stops and stoppage takes place on a fixed frame.
In addition, prior to the invention of the magnetoscope, kinescopes were used which made it possible to film the screen of a receiver in order to be able to store transmissions.
In the kinescope it was necessary to synchronize the cine camera used with the passage of the frames on the receiver screen. This required a very slight increase in the shooting speed compared with a normal camera (25 instead of 24) in the case of European standards and the elimination of one frame out of five in the case of U.S. standards with 30 frames per second.
However, in all these cases, it was necessary to obtain a very great reduction time required to move the film so the film could be moved during a field return time, i.e. approx. 1.6 ms. Although such characteristics were obtained, the cameras were very cumbersome, sensitive and unreliable, so that this process has been neglected.
Although the magnetic tape of a magnetoscope is satisfactory, it is still cumbersome, expensive and liable to deteriorate in time, so that on the basis of these criteria, it is comparable to film.
However, the disk is compact, inexpensive and can be stored almost indefinitely. It has therefore been envisaged to use it for replacing, or at least for keeping a duplicate of films whose storage takes up a great deal of space when kept for a long period.
However, it has been considered desirable to be able to transcribe these video disks into films during a subsequent use in order to be able to utilize cine projection equipment which is widely available, which is not the case with large screen television projection equipment. Thus, interest again exists in the kinescope with the technical limitations described hereinbefore.