Projection engineering (Sept 1929-Nov 1930)

Projection Engineering, June, 1930 Page 11 printing .aperture. By enlarging or reducing the printing aperture, more or less exposure was given the positive film for a uniform running speed of the machine. A refinement developed a few years ago added a new method of light control called the "back shutter," which, as its name implies, consists of a variable aperture shutter located at approximately mid-distance between the printing light and the aperture. The versatility of this method of light control is so great that it permitted dispensing with the varying in width of the printing aperture itself while retaining a great range of light intensities easily controlled from the outside of the apparatus. The "back shutter" proved invaluable in the development of the triple adjustment sound attachment, because it permitted stabilizing the printing aperture to a standard 5/16 inch dimension which is also the height dimension of the triple mattes. The "back shutter" method of light control is applied to the independent printing of both the picture or the sound record, as occasion arises. Now let us turn for a moment to a consideration of the actual manner in which the three masks are arranged so as to control the final result in the (Fig. 3) engage. These pawls are held in place by the triple-tongued spring S (Fig. 3). The slots in the masks are %-inch apart, so that the stroke of the masks is y2-inch. This withdraws the masks sufficiently far back to avoid any interference with the printing light. Fig. 2 demonstrates this more clearly than further explanation. The middle mask is cut away just back of the part that blocks the aperture. This recessed portion comes within 1/16 inch of the front and is arranged so as to avoid any possibility of fringing due to reflections from the sides of the masks. In practice, it insures the line between the picture and sound areas having sharply defined edges. The two side mattes are pulled with a slight rib on the sides adjacent to the middle mask. This rib is %-inch from the front of the mask and protrudes .014-inch from its side. When the middle mask B (Fig. 3) is pulled back, it engages this rib on the side mask and moves it over sideways. The mask is moved .017-inch at the aperture itself. This means that the sound track mask does not cover as much space adjacent to the picture as it did before. Therefore, that portion of the film now uncovered (.017-inch Figs. 4, 5, 6, 7, 8. Illustrating relations of masks to sound track. print. At Fig. 3 is shown the complete unit so that its action can be more clearly visualized. Three masks are employed, the width of the center one being .750 inch and of the two sides masks .107 inch each. They are made so that they fill the 5/16 inch high opening. These masks are made to very close limits, as may be expected, to insure accuracy in their action, and eliminate the possibility of light leaks at their adjacent sides. Each mask operates in accurately milled control slots in the main casting. On the under side, each mask has two slots cut, into which the pawls P wide) receives a double exposure, which results in a black line, or light shield between the picture area and the sound track. Reference to the dimensional drawing (Fig. 9) and to Figs. 4, 5, 6, 7 and 8 will show exactly what goes on. When the middle mask B (Fig. 4) is drawn back it engages the mask A (Fig. 5) and pushes it to the left. In this position the mask A (Fig. 5) covers the sound track proper and the portion of the negative marked Y (Fig. 9) is printed. However, when the sound track is to be printed the mask A (Fig. 6) is set back and the area q a a a a al □ □ .23751 2045 .023 .017" .853" .363" □ □ □ a □ □ □ a .2045 35 MM p-376") Fig. 9. Showing the black line between the sound and picture areas. marked X (Fig. 9) is printed. This overlapping of the two exposures produces the black line between the sound and the picture area. As stated previously, the overlapping is adjusted so that this line has a width of .017inch. To insure clarity in presenting this explanation of the modus operandi of the masks, it was assumed that the film was rewound between the printing of the sound and picture areas. Now let us assume that the picture area is printed as before with the masks set as in Fig. 5. (The negative will be in the forward running position). Then if we desire to print the sound area without rewinding, we remove both the positive and negative films from the takeup spindles and put them on the feed spindles. The printer is again threaded up and the masks set in the position shown in Fig. 8 instead of position 6. Reference to the figures will show how the masks are set for different conditions — it is obvious that the versatility of this sound attachment is all that can be desired. It can also be accepted that its accuracy is exact. S.M.P.E. DINNER IN LONDON THE London Section of the Society of Motion Picture Engineers held its first annual dinner in London in January, this year. Announcement of an offer by Isidore Ostrer, chairman of the GaumontBritish Corporation, to contribute £1,000 towards the establishment of a Trade Research Council and Laboratory formed an important incident at the dinner. Other interesting features of a function which was unique in the annals of the trade were the speeches of Sir Oliver Lodge, F.R.S., the guest of honour, and of Simon Rowson ; the screening of a series of films, including "classic" productions of 1896-1902 and modern sound pictures ; a wonderful demonstration of lighting effects by Holophane, Ltd. ; and an exhibition of acoustical and cinematographic apparatus. The large attendance, under the brilliant chairmanship of Simon Rowson, M.Sc, F.S.S., included leaders of all sections of the trade, besides such distinguished old-timers as Cecil M. Hepworth, Will Barker and J. Williamson. At the end of a long and eventful evening, the opinion was generally expressed that the dinner had proved one of the most interesting and significant as well as unusual functions yet held in connection with the film trade. Welldeserved congratulations were showered upon Mr. Rowson, W. Vinten, Alan J. Williamson, Paul Kimberley and Leslie Eveleigh, to whom, among others, the remarkable success of the evening was largely due.