At the usual rate of exposure 50 ft. of film pass through the camera in a minute, producing about 800 pictures. It is generally possible to break up events into separate episodes of about 125 to 150 ft. each, but nearly all cameras will run for 500 ft. without a break; and one or two have a capacity for over 1,000, or in other words, a twenty-minute story!
We are often asked by a kodak-user, conscious of how unmanageable a quarter-plate film of twelve exposures can become in the dark room when wet: "How on earth can you develop a hundred and fifty feet of film? You tell us you have done it in an extemporised dark room in a guard's van, on the journey between Liverpool and Euston." And yet, given the proper appliances, the task is very simple. Once upon a time we used to wind the film round a large wooden drum which revolved above the developing dish. The bother of this was that the developer was exposed so much to the air that its oxidisation produced stains, unless one was very careful. Development was somewhat uneven, and it was necessary to work by a rather dim light. Then came the pin frame, which can be best understood by the diagram. It consists of a kind of cross frame or wheel, of wood or metal, the spokes of which are studded with a large number of pegs. The one we use is two feet square and takes with ease 160 feet of film, wound carefully round the pegs sensitive side outwards, beginning at the centre. Our actual procedure is as follows: First we cut off two or three inches at one end, as a test with the developer, to see if the exposure is under or over the normal. According to the result of this preliminary test the constituents of the developer must be modified. We then make up a time developer (usually pyro or glycin) in quantity sufficient to fill a stoneware sink twenty-six inches square inside to a depth of about three inches, and immerse the film, frame and all. Pyro-soda is a good developer, especially when exposure has been rather short. It is well to create a little movement in the developing solution, lifting the frame up and down by means of the central handle.
Fig. 72. Cinematograph Film.
Fig. 73. The Pin Frame.
Fig. 74. A Film Wound On The Pin Frame.
When development is adjudged complete the sink is emptied through the drain, and three or four changes of water are poured in before introducing the fixing solution, after which the film is thoroughly washed, treated with a weak solution of glycerine and hung up, still on its frame, to dry. In hot weather it is of course necessary to commence operations with a moment or two immersion in formaline, one ounce to the pint.
Many cameras are claimed by their makers to be available for printing the positive film by contact, but the danger of one film creeping upon the other, as they are drawn together through the apparatus, is very great. If the registration is once lost, the film is valueless for projection purposes, because the broken halves of two adjacent pictures will appear on the screen, the upper one showing legs walking about without bodies, and the lower one ending abruptly with the characters cut off at the waistband. Everything in connection with cinematograph work must be carefully thought out, and executed with scrupulous accuracy. A reliable printing machine cannot be obtained for less than about L35, and must provide against shrinkages in the negative film as well as slight variations of width. The claw movement is preferable. The printing is usually performed with the aid of a fifty-candle-power filament lamp printing from five to ten pictures a second. Development of the positive film follows the same rules as those described for the preparation of the negative. Only, it must be remembered that the positive film is a kind of continuous lantern slide, and therefore a brilliant, plucky effect must be the aim in development - plenty of detail without great density or fog. Each of these little inch pictures may have to cover a screen of twenty or thirty feet, and therefore must allow of an enormous amount of light passing through them.
In the projection lantern the films are kept in due registration by passing over cylinders studded with little cogs or pegs which fit into perforations in the margin of the film and secure regular and even motion without slipping. Films are nearly always perforated by a special machine to the Edison gauge of four perforations to each picture. They may be bought ready perforated before exposure, but for commercial purposes are perforated by the photographer, in order to make sure that his system corresponds throughout with the machines in use. Variations in gauge are a great trouble to the cinematograph lanternist and are frequently due to slight shrinkage of film which has been perforated before development.
Perforation is also of great assistance in securing exact registration when two lengths of films have to be joined together - which is easily done by means of thin strips of celluloid moistened with acetone - or when introducing the black bands during which ordinary title slides are being projected on the screen. But titles are nearly always printed as part of the film itself.
Most of the coloured films hitherto shown have been tinted by hand - and not badly when it is considered that the artist has such a tiny picture to work upon, and the laborious task of dealing with some thousands of pictures, in which the same tints have to be repeated ad infinitum. Some are machine-coloured by a clever contrivance. But the real colour film has arrived. A special shutter is provided with two ray filters, orange-red and blue-green, one for each alternate exposure; and a similar shutter is used for the projecting lantern. The eye seems capable of imagining for itself the complementary colour. The film has to be very highly sensitised, as well as panchromatic, because the pictures must generally be produced, considering the two filters, much faster than the ordinary ones - at least twenty-five to the second. However, one of the most exquisite achievements in colour effects is a film showing a bed of tulips just ready to bloom. The exposures were taken at intervals of a quarter of an hour. Those who have had the pleasure of seeing this film at the cinematograph entertainment when, as if at the bidding of some fairy, the trembling leaves draw further apart, the stalks waver and the buds burst open one by one, to display their richly hued wealth of petals, must agree with us that it is most delightful and beautiful.