Amateur Cine World (May 1936)

(Continued from previous page) () VEV COMI Nt i a | LM to supply me _ with their standard stainless steel front plate, channelled out to the width of the picture, with guide pins at the sides, and with a modified hinged pressure plate, using the channelled pressure pad of the standard Home Movie machine, this fitting being at their suggestion. In this new gate, the film was held only at the extreme edges, as in the standard Home Movie machine. Improved Plate Now Fitted On fitting the gate to the projector, and running a length of film, joined into an endless band, continuously through the machine for some five minutes or so, during which time the film passed through the gate some fifty or sixty times, I found no scratching at all on the picture area. Since fitting this new gate, I have had no scratching in the projector at all. I see that the newest 200 B projectors are fitted with the improved front plate to the gate and the back part now bears on the film only at the edges. So much for projection and I turn now to the camera. Here, there is normally only one opportunity for trouble to occur, as the film only passes through once, except in the comparatively rare instances of multiple exposure. But the undeveloped film is exceedingly sensitive to pressure and friction, quite distinct from actual scoring SCRATCH oz 9.5mm. or scratching, which causes lines and marking almost exactly as if light had affected the emulsion, showing up on development as black lines in the case of a negative, which are reversed to white lines in the case of reversal film. A scratch, on the other hand, will appear as a fine black line or a wider line with possibly a clear central line on either negative or reversal stock. The reason why a scratch appears black and not clear, is that the edges of the scratch are, as it were, ploughed up, giving extra thickness to the film and so appearing of greater density than the surrounding area. This enables one to distinguish between the two forms of marking. Removing Roughness from Gate With the Pathe Motocamera B, I found that no scratching was caused by the camera, except for a slight roughness on part of the gate, which I easily removed with the aid of a fine-cut oil-stone, since when I have been able to run film through the camera without a scratch, which I tested by an endless band of film, as in the case of the projector. Pressure and friction markings cannot be seen in this way, as they only show up after development, but I have never had trouble from this cause, and it is unlikely to arise as the pressure of the gate is distributed over a comparatively large area. The chief cause of scratching in the camera is undoubtedly due to the chargers which almost every 9.5 mm. camera employs. However, for those who keep a number of chargers by them, and reload at home, there is a simple remedy for this, involving a slight modification to the charger, easily carried out by anyone handy with their fingers. By putting in a roll of old film, and loading the charger into the camera, but keeping the charger lid off, the behaviour of the film as it runs through the camera can be studied. From this I learnt that the emulsion of the film comes into contact in three places. Two Sources of Trouble The openings of the two channels through which the film leaves and re-enters the charger are two of the sources, this being caused by the intermittent movement of the film through the gate which has the effect of making it touch momentarily at both top and bottom apertures. This gives rise to short disconnected lines running in the direction of the length of the film, but usually not extending over the sprocket holes. In the case of the new model Dekko, rollers are fitted at the top and bottom of the gate which effectually prevents the film touching at these points. In both the Pathe and the Dekko camera, the film does not touch the inside of the channel except on the back where marking will not occur, and in the new Dekko, it does not touch at all except in the one remaining place. This is common to all cameras, as it is purely (Continued on page 83) Under exposure gives semi silhouette effect suggestive of declining day, but remember that not all subjects can be successfully treated in this way.