The Moving picture world (December 1920)

922 MOVING PICTURE WORLD December 18, 1920 the boiled-down, carefully compiled and arranged extract of all that is known, not merely by one man, but by all men, of the subject dealt with up to date. We hope some of these fine days to have the pleasure of meeting the Manitoba officials personally, and of visiting the city of Winnipeg, though when that will be we cannot say, though we do hope to be able to "make" the Toronto meeting of the Canadian inspectors next year in Toronto. How to Get the Angle In a letter signed by G. W. Bennewitz and E. W. Ledyard, projectionists, the Strand Theatre. Sioux Falls, South Dakota, we have the following: In going over the various articles on crater angle, brother Ledyard and myself found a contradiction. The attached drawings illustrate the same, show an easy method of getting correct angle and show the wrong and right angle. In April 10 issue appears an article under the caption, "Should Get Another Lens," in wnich, in first paragraph after sub-title "The Idea Is ," the statement is made that the crater angle should be a fifty-three angle with the face of the condenser. Figure one shows what this would result in, it being a true 55 degree angle with the condenser face. In April 17 Issue, In questions and answers. No. 8 reads: Question: What Is the most economical angle of crater to lens? Answer: 35 degrees. In July 10 issue, "How Did He Do It?", brother Dobson "orgot to mention the fact that the crater image would be inverted when projected through a pin hole in the lamphouse door. Most of us know this, but there are still those who do not, and when they tried the experiment they would find the image to be upside down and would declare It a fake. In August 14 issue, "Crater Angle Diagram" Is not of much use. as you say, since the 55 degree angle line Is not Included. Brother Creamer had the right Idea and was working from the optical axis, but his diagram would give the impression that a 66 degree angle was best. A» Regards DrnwInRi. And now as regards attached drawings, Figure 1 is a true 55-degree angle with the face of the condenser, which as you will o»-e at a glance, is very far from being economical. Figure 2 is a true 55 degree angle with the optical axis, which is the correct angle is drawn to show how the crater image will look when inverted by projection through a pin hole. A shows the image when projected through a pin hole in the left hand lamphouse door (meaning left hand side of a lamphouse when viewed from the rear, I suppose. — Ed). B is the same when projected through the right hand lamphouse door . C shows the tips of the crater images; the line drawn to represent the optical axis should be drawn through this point. Figure 4 shows how an ordinary 2-foot rule may be used to lay off the 55-degree angle. When the rule is opened so that from the 6-inch mark on one leg and the 18-inch mark on the other, the distance is 5 17-32 inches, the Inside edges of the rule will represent a true 55-degree angle. Figure 5 shows how to lay off the angle with a plain ruler. Have point C at tip of crater, Figure 3. then measure back six inches along the optical axis and draw line C B. Measure six Inches from point C to point A and when you have a distance of 5 17-32 inches between A and B line AC will be the desired 55-degree angle. and. as Is plain to be seen, a far more economical angle than the one shown In Fig. 1. Figure 3 is not a true 55 degree angle, but Figute 6 illustrates another method of laying out the 55-degree angle. Secure a sheet of cardboard about six by eight inches in dimension, cutting side AB with a straightedge. Draw line C D at right angles to side A B, then lay out line F E at a 55-degree angle to line C D. Then strike an arc and when the crater is well burned in and the light properly adjusted at the spot, pull table switch and allow crater to cool. Open both lamphouse doors and place the cardboard inside the lamphouse, with side A B against the front wall or the condenser mount, and against the side of the carbons. Make a line on the cardboard by drawing a pencil across the face of the crater. If this line is parallel with line FE all is well. If not then re-adjust carbon and burn crater until you get it right, so that the two lines have the same angle. As soon as that point is reached in the proceedings, project the crater .image and mark the angle on floor or wall, wherever you are projecting the image. We Are Obliged We are obliged to you boys for your excellent drawings; also for calling attention to errors of the past. That they were nothing more than inadvertent misstatements is self evident, but they should nevertheless not be allowed to stand. The only flaw in your plan is the failure to describe the method of locating the optical axis line when describing procedure as to Figure 5. If the image be projected straight to the projection room wall, or a screen on the lamphouse door of the left projector, the method is simple, but if theprojection be to the ceiling or floor it is more complicated, and we would ourselves have to have such a projection before us in order to dope the thing out. He Cuts a V Groove Donald I. Brown, chief projectionist, Victory Theatre, Putman, Connecticut, says : In last number of the "World" I noticed a projectionist claims that by putting the carbon in the lamp with the trade mark side toward the lens he gets better results. Ia he using A. C. or D. C.? I use White A. C. special carbons, pulling sixty amperes through a Fort Wayne Compensarc, of which we have two, and find that by filing a small grove in the upper carbon, using a three-cornered file for the purpose, the crater is kept more even and the arc burns a great deal steadier. Cannot say as to whether or not this has any bearing on the trademark matter or not, but as you say????? Let us hear from others. And now I am going to ask you once more to PLEASE find out why I have not received my handbook. It was ordered just one year ago and has not showed up yet. Why??? Possessed of Patience Well, brother Brown, if you ordered a handbook a year ago and have not yet received it you are entitled to go right up to the very head of the class as being possessed of the patience of our some-timeago ancestor Job, though how "Job" is made into "Jobe" I could never understand The matter will be immediately investigated. Most men would have torn our reputation to very fine shreds and have purchased thin sheet asbestos on which to write the complaint had such a thing happened to them. It is up to the book department. Get busily busy, gentlemen. As to the groove, it was tried out and discarded years ago. At one time a carbon manufacturer, the CCW.6. B Seimens, I think it was, made their carbons with a V groove on one side, but they soon discontinued it.