The motion picture projectionist (Oct 1927-Sept 1928)

34 The Motion Picture Projectionist October, 1927 what happens to the film when the framing lever is given a sharp, downward blow on a projector where the complete carriage moves as one unit. Figure 15 shows the same damaging result on a model on which the intermittent sprocket only moves in synchronism with the framing lever. Film Loops Excessively large upper or lower loops either cause a rattle in the film guard above or allow the film to drag in any oil which may be present below. The film also has a tendency to jump the sprockets, which can take place if the idlers are set too far from the sprockets. The practice of resetting loops while the projector is running should be discouraged as in many cases the sprocket teeth strike outside of the perforations, or otherwise damage the film. Fig. 14. ing the on this kink in by the carefully Suddenly jerkframing lever machine puts * the film shown arrow. Frairu and slowly. Film Tracks or Trap Shoes Many scratches are caused by worn film tracks, or trapshoes as they are known on one of the projectors, allowing the face of the film to scrape against the recessed aperture plate. Such tracks or trap-shoes together with all tension shoes or door pads that show a "wavy" or badly worndown surface, should be replaced by new ones. Fig. 15. On this type of projector, also in common use. buckling of the film will occur if framing is done too rapidly. Fire or Valve Rollers The valve rollers of both magazines should always be kept clean. Care should be taken to see that they revolve freely as a sticking roller can cause bad emulsion scratches especially if it is worn, thereby allowing the center of the roller to come in direct contact with the face of the film. This is especially true of the upper magazine rollers around which dirt and small pieces of film very often accumulate. Adjustment of Film Trap Door On one make of projection machine the film trap door is designed so that it can be easily removed by merely lifting it from its holder. In replacing this film trap door care should be taken to see that it is seated properly, as unless this is done one is liable to ruin the intermittent sprocket, bend the shaft as well as ruin the film which happens to be running through the projector at the time. Strippers on Upper and Lower Sprockets On some projectors, so called strippers or stripping plates are provided to prevent, by any chance, the film from winding around or "following" the sprockets as well as to remove any accumulation of dirt that may tend to form at either side of the sprocket teeth. In resetting these strippers after the replacement of sprockets, ex treme care must be taken to see that they do not come in contact with the teeth as this will cause the teeth to wear to a sharp edge which will damage any film coming in contact with it. Unnecessary Oiling Flooding the mechanism with oil is unnecessary and causes oil to get on the film. Dust then adheres to the film making good clear projection impossible. This practice also is a fire hazard as oily film will catch fire a great deal easier than that which is clean. Aside from the intermittent case, one drop of good oil in each oil hole will be sufficient for the average day's run. One Method of Tracing Film Damage Film damage can sometimes be more easily traced if it will be remembered that certain projectors run the film emulsion or dull side against all three sprockets, while on others the support or shiny side, only touches the sprockets. For example ; if film is received showing tooth marks on the emulsion side, it is fairly simple to determine on what make or makes of projectors this film has been run, especially if the investigator has familiarized himself with the different types of sprocket teeth. Why Film Should be Waxed In conclusion, special attention is drawn to the desirability of waxing new prints along the perforations to prevent unsteadiness and premature breakdown. In making the light sensitive emulsion of motion pictur film one of the chief ingredients is gelatin — a substance which readily absorbs and gives off moisture. In freshly developed film the gelatin contains a considerably higher percentage of moisture than is found in seasoned film, and when in this condition it is easily affected by heat, tending to make it soft and tacky particularly in a moist atmosphere. The first point at which new film comes in contact with unusual temperature is at the aperture plate of the projector where the light is concentrated, producing heat to a degree which softens the gelatin and causes it to collect on the tension springs or shoes where it rapidly dries and forms a flint-like deposit. As the new film is projected, the hardened deposit of gelatin continues to accumulate and offers further resistance, causing scratches along the perforations. As the resistance increases there is the added danger of the teeth of the intermittent sprocket tearing and damaging the perforations, sometimes to an extent where injury to the print is irreparable. Careful waxing produces, under the action of heat, a smooth and polished surface on the gelatin along the perforations ; provides against undue straining during the first projections of new prints ; materially benefits successive runs, and greatly prolongs the commercial life of the prints. Cold wax should never be used as it is impossible to apply it evenly. There is also the danger with the cold method of over-waxing with the result that, in contact with the heated pressure springs, the wax melts and spreads over the picture. A very slight application is all that is necessary and is best accomplished by a waxing machine which deposits a thin layer of hot wax along the perforations. New prints treated in this manner require no further waxing.