International projectionist (Jan-Dec 1947)

Projection Data Charts By ROBERT ALLEN MITCHELL Addenda to Data Forms 1 A and 1 B The publication of these addenda concludes this series of seven articles. This series was noteworthy for, among other things, the fact that it was conceived and executed by a projectionist working daily at his trade, that it represents the most comprehensive effort of its kind, and it affords the craft the first real working basis for cataloguing every unit of equipment used in the sight-sound projection process. HERE are a few additional electrical formulae that the projectionist may find useful in connection with carbon arc circuits. To determine the resultant voltage of d.c. generators or rectifiers connected in series: Rule: To find the total voltage of series-connected current sources, add the voltage outputs of the separate current sources. Formula: els e2, etc are the separate voltages) : E ex + e2 + e3 + . . . en To determine the resultant voltage of d.c. generators or rectifiers connected in parallel (shunt) : Rule: To find the total voltage of shunt-connected current sources, add the voltage outputs of the separate current sources. Divide the sum by the number of current sources. Formula (ev e2, etc., are the separate voltages; n is the number of generators or rectifiers) : e1 + e„ + e3 + . . . en E = ■ n To determine the resultant available restrictions at the moment, Folsey feels most of them can eventually be overcome. John Arnold, head of the M-G-M camera department, describes the effect of reflected lighting as "comparable to the latest practices in fluorescent lighting. Whatever measure of success is achieved with the Folsey method, by himself and others, during the coming months, projectionists have cause for satisfaction in the knowledge that there should be a definite improvement in the theatre screen image of interiors. Several years ago the screen image suffered by reason of the widespread use by cameramen of the "arty" type of softfocus lighting which was supposed to invest a given sequence with "mood" and so-called artistic appeal. The "mood" induced by such camerawork on the reproduction end was the feeling of anger and frustration on the part of projectionists, most of whom felt that the pictures were all being shot during a dense fog. Print Density Blamed Cameramen were quick to pass the buck anent these projection difficulties to the laboratories, the story being that sloppy lab work in terms of incorrect print density not only was riling projectionists but was actually ruining those photographic effects which were achieved only after careful planning and much arduous work in setting up the lighting units on a set. Wherever the fault lay, it is a fact that even in the de luxe theatres high-intensity arcs pulling 130 amps and more were unable to penetrate the murk that seemed to envelop the screen image. Another pet peeve of projectionists was the sloppy work exhibited by certain color picture, produced by processes which are of comparatively recent development. Whether these faults may be ascribed to inefficient set lighting or to a lack of control in the printing process is not known ; but projectionists recall such releases with a shudder. All color processes have improved greatly over the past couple years, particularly in the laboratory work, and today many color films are better lighted than some black-and-white pictures which are turned out by certain cinematographers who seem not to be aware as yet that the vogue for low-key set lighting has long since passed. Projection people do not insist that the entire picture area be brilliantly lighted, and they admit the justification for gradations of light that will definitely enhance the mood of a certain sequence. They do insist, however, and rightly so, that the characters and vital elements of a set be so lighted as to be visible when projected by a high-intensity light source. amperage of direct-current generators or rectifiers connected in series: Rule: To find the total available amperage of series-connected current sources add the available amperages of the separate current sources. Divide by the number of current sources. Formula (ils i„ etc., are the separate available amperages; n is the number of generators or rectifiers) : ij -f i2 + i3 + . . . in I = n To determine the resultant available amperage of direct-current generators 01 rectifiers connected in parallel (shunt) : Rule: To find the total available amperage of shunt-connected current sources add the available amperages of the separate current sources. Formula (i1, i.„ etc. are the separate available amperages) : I = ii H i? + is + • • • *n To determine the resultant resistance in ohms of resistance units connected in series: Rule: To find the total ohmic resistance of resistance units connected in series add the ohmic resistances of the separate resistance units. Formula (r15 r,, etc. are the separate resistances) : R = rx + r2 + r3 + . . . rn To determine the resultant resistance in ohms of resistance units connected in parallel (shunt) : Rule: To find the total ohmic resistance of resistance units connected in shunt divide 1 by each resistance. Add the quotients. Divide 1 by the sum so obtained. Formula (r,, r2, etc. are the separate resistances) : 1 R= ■ 1 1 — + 1 r1 r2 r3 rn To determine the horsepower corresponding to electrical power: Rule: To find horsepower multiply volts by amperes by 0.00134. Formula (E represents volts: I represents amperes) : H.P. = 0.00134 EI i ADDENDA TO DATA FORM 6 Appended are a few additional formulae in connection with projection and screen data. To determine the change of brightness of a picture with a change of throw, the lamps and lenses remaining the same: Rule: To find picture-brightness change with a change of throw divide (Continued on page 27) 10 INTERNATIONAL PROJECTIONIST December 1947