Projection engineering (Jan 1932-Mar 1933)

Page 16 PROJECTION ENGINEERING color master is at full brilliancy, a second at Y\ brilliancy, a third at y2 brilliancy, etc., should these circuits be dimmed out by the color master, they will start dimming at the same time and proportionally change so that they reach the blackout position at the same time. This is in contrast to the operation of the standard interlock type of color master in which a similar operation would result in the circuit at full brilliancy being dimmed until it corresponded to the one at % bnl~ liancy at which point the second circuit would interlock with the color master and both these circuits travel until they reached half brilliancy where the thirf' circuit would interlock and finally all would block out together. This oftentimes resulted in a spotty effect and is undesirable. By using an electrical color master rather than a mechanical color master, a proportional dimming effect is accomplished as previously described. Master Control In order to obtain grand master control, the pilot switch on the color master section is transferred from the hotbus position to the grand master position which connects the circuits on the color master to a master generator. By varying the voltage on this master generator, the potential impressed on the color master is varied, thus causing a proportional change similar to that previously described for all the circuits connected to the grand master. Motor operation is provided for the dimming fader on the Los Angeles theatre job so that it is possible for the operator to change from one effect to another by simply pushing a small telephone switch starting the motor drive. This motor drive is so provided with limit switches that it will travel to the next succeeding scene at which point it will stop and will not restart again until the operator pushes the "start" button. This allows an easy means of obtaining remote control of the intensity of all the lighting circuits in the theatre. In the old type of multi-preset board it was entirely possible to obtain remote control scene changes, but it was impossible to obtain a preset of the intensities, it being necessary for the operator to set the dimmers beforehand or to change when changing from one effect to the other. By using the thermionic tube control, it is possible to preset the dimming as well as to preset the circuits which are to be used and furthermore, obtain remote control of these circuits if it is desired. This is of special advantage in some moving picture houses where it is desirable to control the light from the projection room and at the same time have a switchboard on the stage floor which can be used in case of stage presentation work. Remote Control In the Los Angeles theatre, the remote control board at the stage floor allowed the stage switchboard operator to have full control of the color masters for the auditorium circuit and in addition to this allowed him to change the lighting effects in the auditorium for five presets, which had previously been determined by means of the switchboard located in the projection room. Furthermore, by means of the color masters, it was possible for the operator to dim out any particular color from any scene that had previously been preset thus giving a very flexible control. The previous description covers the tube type switchboard which was installed in the Los Angeles theatre and is typical of this type of control. Due to the rapid development in this art, at least one other scheme has already been conceived. Instead of a grid-glow type tube, a vacuum tube of a rather large plate capacity is used and a motor-generator set supplies 500 volts direct current to the plates. The output is regulated by grid control of these tubes. That is, the 500 volts from the generator is connected in series with the vacuum tube and the direct-current coil of the reactor. Thus by varying the impedance of the vacuum tube by change of grid potential, the amount of direct current that is allowed to pass through the d-c. coil of the reactor is changed. The control equipment, that is, the potentiometer setup is practically a duplicate of that used for the Los Angeles theatre, the new developments affecting the tube units rather than the control. Scene Changes Another advancement has been in the method of control by which it is now possible for a switchboard to be built wherein the operator may change from any one scene to any other scene and get a gradual shading effect from one to the other or obtain a flashing effect as previously described. The Los Angeles theatre was built before this development so that in this job it was necessary to fade from one scene to the next succeeding scene. This new development allows a much more flexible means of control due to the fact that in stage presentation work it is often desirable to repeat an effect and with this type of control, it is possible to do this as often as is desired and to fade into this effect from any other that may be in progress. Another interesting development that has recently been brought forth, the first application of which is for the control lighting of the Buckingham Fountain in Chicago, provides a continuous preset program which is laid out in advance for an evening's performance. This is accomplished by means of an insulating track on which there has been drawn a conducting path. This moves and is continuously in contact with a potentiometer similar to the control potentiometers for the tube units. Thus by varying the location of the conducting strip on the moving track, a variable preset potential is obtained which correspondingly changes the output of the tube unit and a change in the intensity of the lighting circuit results. While this is developed for floodlighting control, it may be used for such an application as varying the lighting of a theatre according to a definite program for the overture. It could also be used for providing a light change program for the patrons at the time between the opening of the house and the beginning of the performance. This program is motor driven and can be started and allowed to run for a definite period of time after which by means of a transfer relay, the control could be transferred back to the regular stage switchboard for use in connection with the picture or the stage presentation. In summarizing, it may be said that the application of thermionic tubes to theatre dimming has made possible a stage board giving the following very desirable features : 1. Presetting of intensity for any desired number of scenes. 2. Proportional dimming. 3. A light compact board using telephone switches thus insuring ease of operation with added insurance of proven reliability of this type of equipment. 4. Low control voltage (less than 50 v. d-c.) allows use of telephone cable for control wiring. 5. Remote control easily added. In fact, the field of the application of tube control to lighting, is in its very infancy and due to the rapid development in tubes, as we have witnessed in the past in the radio field, a great deal may be expected from this type of equipment. SPRING MEETING OF S. M. P. E. The Board of Governors of the Society of Motion Picture Engineers has voted that the spring meeting of the society shall be held in either Washington or New York City, with a tentative date set for May 9 to 12. Choice between these two cities will be made by the members of the Society and ballots have been mailed to the members for their votes, according to W. C. Kunzmann, chairman of the convention committee.