The Bioscope (Jan-Mar 1913)

THE Broscore, JANUARY 16, 1913. HELP IN TROUBLE. FOR PROPRIETORS, MANAGERS, AND OPERATORS. CINELUX writes: “I have heard that incandescent paraffin burners are now made giving 2,500 candle-power (I have one of 500 candlepower for lighting a hall). Can you say if such could be used for projecting? Would 2,5co candle-power give sufficient light for the projection of a picture to cover a 9 ft. square screen at 100 ft. throw, or to project from behind piciure at 20 ft. distance?” We regret, CINELUX, very much to say that, although very high candle-power paraffin burners are made, they are totally unsuitable for projection purposes. There is no limit to the candle-power one can obtain with any form of illuminant, but, unfortunately, it means the duphcation of burners giving a very large area of illumination. Now, for projection purposes a concentrated light is necessary, and one as nearly as possible approaching Euclid’s definition of a point would be ideal for the purpose. The electric arc lamp is, without doubt, the nearest practical approach to this, and for that reason a lower candle-power obtained with an electric arc is superior to many higher powers generated by othcr means. As you have no electric light available. we would recommend that the oxy-hydrogen limelight be used. If you can obtain town gas. you could use this in conjunction with compressed oxygen, which can be purchased in cylinders. [ailing your having town gas, you can use coal yas and oxygen both compressed in cyl nd.rs. High candle-power limelight jets can be obtained that will give a fairly concentrated light of between 2,000 candle-power and 2,509 candle-power, and which, although not equal to clectricity, would nevertheless project you a very satisfactory picture under either of the conditions you mention. * * * “AH.” who intends entering the cinematograph business, writes as follows: What would be the approximate cost of projector and c¢leciric light generator set, the latter to be driven by a petrol engine? Also the cost of a portable theatre suitable for moving from place to place if my original site proved unsatisfactory? Would you advise me to learn operating. and, if 50, where is there a te oogle A new cinematograph projector of the Maltese Cross type would cost you between £35 and £50, depending upon the manufacture, but you would be advised to write to the makers of machines whose advertisements will be found in our pages for particulars and prices of their goods. Regarding a petrol generating plant, the price would depend entirely upon the output, but one capable of giving you about 40 amperes for the arc and 30 amperes for general lighting at a pressure of 65 volts would cost you somewhere between £130 and £150. We regret we have little information by us regarding portable theatres, but we believe that Messrs. Heath, of Manchester, specialise in temporary structures and in buildings of a more or less portable character. It would certainly be advisable for you to learn operating. You might write to the Secretary of the London Bioscope School, St. Martin’s Court, W.C. a er “LJ.” writes as follows: “ My pictures have lately taken to jump very much upon the screen. This has been a very gradual development over the past six months. Could you advise me on the cause of the trouble? I would add that the machine is a Maltese Cross one?” The trouble is, in all probability, due to wear in the Maltese Cross, which can be taken up by adjustment, or to the gate springs having lost their tension. If the Maltese Cross be at fault, you can test this by feeling the intermittent sprocket-—that is, the one just below the gate and connected to the Maltese Cross shaft. Turn the handle of the machine a revolution or two, and note the intermittent action of the sprocket. Stop the machine at a point where the sprocket is stationary, and sec if there is any sign of slackness in the sprocket wheels— not lateral movement or end play, of which there is bound to be a little, but a rotary movement. If the Maltese Cross be properly adjusted in relation to the actuating cam, there should be no sign of slackness, the sprocket wheel being absolutely locked in position. If there be movement here, which in all probability will be the case, you must look to the method for taking this up. In some machines the Maltese Cross shaft