Home Movies and Home Talkies (Jun 1933-May 1934)

174 HOME MOVIES & HOME TALKIES HOME PROCESSING OF ,i,%. *' NEG.-POS/' CINE FILM By ''RIVERSIDE'' 3.— Printer and Test Strips EDITOR'S NOTE : In the series of articles of which this is the third, the processing of 16-mm. negative-positive film is being treated. Later articles will deal with 9J and 16-mm. Reversal stock The Printer THE printer, constructed from an old projector, is illustrated in Fig. 1. The main features are here outlined, as these are essential in converting any other type of projector. It is driven by a fan motor through the belt B, the sizes of the wheels being selected for printing eight frames per second. A small stroboscope is fitted to the driving wheel for checking the sjaeed. The negative film N is taken off the top reel and the unexposed positive P from a reel in a box on the left by the feed sjirocket F. The two films are jDulled intermittently through the gate by the claws. Adequate contact is provided by the springs on the slide in front of the gate. Below the gate, the films divide and are received into cardboard boxes, ready for re-winding. The optical system consists of a lamp L behind a groiuid-glass screen. The light passes through the negative and illuminates the positive. Sufficient light passes througli the latter foithe image to be observed through a hole cut in the slide by means of a right-angled prism. In between is placed a red filter so that no actinic light passes out of the printing box and fogs the unexi^osed positive. If necessary, the aperture in the gate must be widened to ensure that the whole image is printed. It will be seen that the exposed positive comes out of the gate above the bottom of the latter : this, to permit a jiunch in the side of the negative to allow a contact (terminals T) to come forward and operate a relay in the commutator box wlien a change of intensity in the printer light is required. The reasons for this complicated switching is to ensure that successive shots in the prints are matched in average density, or otherwise adjusted to make up for \ariations in camera exposure or development or batches of negative film. The separate adjustment of the printer light for every piece of negative is, of course, standard professional practice. The commutator board for this control of printer light is shown in Fig. 2. It consists of 25 vertical bars, each taken to a continuously rotating switch operated one step at a time by the relay operated by the contact below the gate, and 16 horizontal bars (behind the panel) tapped on to a resistance in series with the lamp L. By inserting a terminal in one of the holes, as shown in Fig. 2, for all the vertical bars, the resistance required for a partic\ilar strip of negative is anticipated and is instantly switched into circuit by the relay. At the top of each vertical bar is a hole covering a red lamp which indicates, by lighting, which vertical bar is in Fig. 1.— The printer is constructed from an old projector circuit. A small push-button in parallel with the gate contact is used to step the relay to the correct starting position as indicated by the small lamps. When a lap -dissolve is made between two negatives of widely differing densities the transmission must be made uniformly through the mix, occupying perhaps only 6 in. of film. kSuch a transition is indicated by the I'ow of terminals in the centre of Fig. 2. There has been found no difficulty in passing over-lapping negatives with the positive througli the gate. Great care has, however, to be exercised in previously winding the double negatives on the upjier reel, as they can only be stuck together at the end which goes through the gate first. On one occasion, when the negati\'e sjirocket holes had been Fig. 2.— This commutator board is for automatically adjusting the intensity of the printer light to compensate different average densities of negative damaged in a projector, a print was made running backwards ; professional release-prints are also printed to -and -fro to obviate negative rewinding. In printing " Valse Triste," Riverside's first all-amateur processed film, there were about 60 changes of printer light to be anticipated on the commutator board during the eight minutes required for printing. Most of these changes were required during lap-dissolves and where the incidence of double thickness of negative base required an increase of illumination. Test Strips To make all the above complication worth while it is essential to control the procedure with scientific data obtained from test strips. These are of two kinds, gatnnia strips and printer strips. The latter is a test made in the printer for every piece of negative, and consists of about 6 in. of positive printed with increasing printer light, such as is obtained by plugging terminals as in the centre of Fig. 2 and stepping the relay with the push-button after every two or three frame-; as tlie negative goes through the gate. Naturally, when a number of negatives are to be printed in sequence, they are all tested in sequence and developed according to the standard method. In Fig. 3 are shown two such examples (c) and {d), one more or less diagrammatic, although shot on pan-neg., the other pictorial. By inspection, the most suitable printing illumination is selected and the number noted for further reference when the release print is processed. The gamma strip is shown at (a). Fig. 3, and is obtained by exposing the tail-end of every negative reel to a standard source of illiunination. a gas -filled lamp at a known distance (3 metres) for a gi\'en time, 4 seconds, through a glass plate, of appearance similar to (o), having sections of graduated density. B.\' measuring