Motion Picture News (Dec 1920-Feb 1921)

900 (Equipment Service) Motion Picture New jection lens. Putting in the proper condenser bends all the rays so that they pass through the slide and enter the projection lens. When parallel rays strike the surface of a simple lens that point on the opposite side of the lens at which the rays meet, is known as the " focal point." The " focus " of a lens is the distance from the focal point to the lens itself. In reality, it is the distance from the focal point to the optical center of the lens, which is a point within the glass itself. {To be continued) Wants Data on Projection Room L. E., Shelbyville, Indiana, writes : Please answer the following questions. We are building a theatre, the distance from booth to curtain is 140 feet. What size picture would be best to show and how much larger should the screen be than the picture? We are wiring the booth with a threewire system. What size wire should we use? We expect to use No. 4. Is this sufficient or should we use No. 2? We expect to use a generator. Please advise us whether it would be best to use a single or three phase and what amperage and voltage would you recommend? Reply: Although you give us no floor plan to indicate the shape of your theatre and the seating arrangements we would judge that a 13 x 1514 ft. screen would be plenty large enough. Whatever size -you decide on don't select one too large. There is a certain clique of theatre managers who believe in a super-large screen sometimes running to 24 ft. In a house like the Capitol in New York City with its balcony 200 feet away from the screen it is necessary to have a monster screen but otherwise there is every reason why they should be discountenanced. The screen should be 10 inches wider than the picture. No. 4 wire is large enough to handle anything you would be called on to use in the projection room. If you have three phase current available then use it by all means. Motor generator sets are supplied with motors of one, two or three phases but the three phase is preferable to the single phase because of its lower cost, its higher efficiency and the fact that the power company prefers to keep the regulation of its system as good as possible. With a motor operating on one side of a three phase system there is apt to be trouble from unbalancing. You would want to get the 70 ampere motor generator set. This will allow you to draw that current if you need it. Whether you will or not will depend on several things ; amongst them being the skill of your projectionist, the film itself and the condition of the screen. Don't worry about the voltage of the generator. Leave that to the manufacturers. The motor generator set you want is the one made for motion picture work and the voltage characteristic is such that when you adjust the set for the right current the voltage will take care of itself. Splicing Films with Odd Frame Lines From S. B., Crete, Neb., comes this query: I am enclosing two pieces of film which I am positive cannot be patched in such a way as to absolutely prevent a misframe. However, our other projectionist says that in a former issue of the News there was explained a method by which it may be done. If so will you please advise me. We have a Baird machine and by framing one piece of film I find it impossible to frame the other without moving the framer. Answer : One of your pieces of film has its frame line come in the center of the perforation and the other has its line come between two perforations. It is an absolute impossibility to patch these two pieces so that the strip will remain in frame without adjustment. A few cameras still have the old non-standard frame line but they are gradually being replaced by standard instruments. Name Plate on Generator Bothers Him J. A., Hawaii, writes: In your Projection Department there has been running a series of lessons on Elementary Electricity. I have taken great pleasure in reading and studying them. I would like to have you explain a few questions regarding my generator. I have an Allis Chalmers direct-current generator on which is attached a plate which reads as follows: D. C. Generator Continuous Duty. Serial No. 3K6089.2 K. W— 4. R.P.M.— 1800. Volts. No Load —116 Amperes 33.3. Volts full load— 120 Temp-rise, full load continuous winding — 40°C. Comm.— 45°C. 25% Overload— 2 hrs.— Windings— 55° C Comm. 60°C. I do not understand the last two lines having to do with temperatures. I have also noticed that there are three wires leading from the generator. I am quite sure they are positive, negative, and neutral, but as there are no marks to indicate which is positive and negative how am I to know ? After finding this out to which lead should the field rheostat be connected to regulate the voltage? I have looked over the wiring diagram for a 35 amp. outfit manufactured by the G-E Co., and I noticed that the field rheostat is always connected to the positive wire. Does this apply to all makes of generators. Reply: The name plate of your generator states that when you run the machine at full load for a long time (continuously) the temperature rise in the windings should not rise more than 40°C above room temperature and that the commutator should not get warmer than 45 °C above the same standard. With a 25% overload for 2 hours the machine will naturally run still warmer but this, according to the name plate, should not become more than 55°C and 60°C respectively for windings and commutators. If these figures are exceeded something is wrong. As you know a d. c. generator will rotate in either direction according to the dispositio,n c the connecting wires. As received from tb factory these machines are connected to tate counter-clockwise when viewed from pulley-end. To accomplish this the field nection is usually carried to the positive wi If it is changed to the negative the rotation be changed about. If the field terminals are reversed the direc tion of rotation will be reversed, but other .vis there will be no difference in the general o: ra tion. Get a direct current ammeter. The ten. will be marked plus and minus. Put the wirj on either way, just touching one terminal one wire. If the ammeter registers the on the plus terminal is plus, but if the need on the meter tends to go backwards you hav the polarity reversed. Exchange of United Artists Is Simplexized Among the prominent distributing companies' exchanges, located in the Godfrg Building at 729 Seventh Avenue, is that of the United Artists CCorporation. This exchange; located on the ninth floor of the world's busies! film building, is that through which Mary Pick* ford's, Charlie Chaplin's, Douglas Fairbank'* and D. W. Griffith's productions are released ana distributed. 1 One of the features connected with this establishment is the reviewing room. This room, which is 12 feet wide by 25 feet long, is finished in old rose with artistic panelling on the walls, while the concave ceiling, lighted with indirect domes. A group of comfortable chairs are included in the furnishings of this splendid little reviewing room, which boasts of perfect projection upon ; 6x8 white plaster screen which is located at thi extreme end of the room. A most artistic border surrounds the picture screen, giving the exhibition a real theatrical atmosphere. It is here that private screenings are staged of all United Artists' products, for the personal attention of Mr. Hiram Abram^ the president of the organization. The projection room connected with this reviewing room is operated under the direction of Mr. Al Kaufman, a well-known New York Cityprojectionist, whose activities during thre& years' service with D. W. Griffith are well known in projection circles. In this projectio: room are installed two Type " S " Simplex Pro jeclors with motor-driven attachments. '^4 Two views of the projection room of United Artists zviih the Simplcxes on the right I