CHAPTER IV
THE CAMERA AND HOW TO USE IT
Having examined the mechanism of the moving-picture camera, and the broad principles upon which it works, we must now study the way to use it.
The first step is to load the film box, an operation which must be carried out in the dark room. The film is sold as a rule in standardised lengths, such as 100, 200, 350 feet, etc. With the ordinary type of camera the 100 or 200 feet lengths are used. For topical work either are quite adequate as a rule.
As has been said, the film is supplied perforated and ready for use. Many firms that sell the "stock," as the unexposed film is called, attach a blank or unsensitized "lead" to one end of the roll, for the purpose of "threading-up" the camera. If this is not supplied, and if the operator wishes to avoid the waste of 2 or 3 feet of sensitized ribbon, the deficiency can easily be remedied. For the blank "lead" all that is required is about 3 feet of useless or spoiled film which, however, should not be torn or cracked. The emulsion at one end of this should be scraped off for a distance of about ¼ inch. A pocket knife will do this very efficiently. The blank should then be laid flat upon the table, emulsion side uppermost, preferably upon a sheet of glass which secures a smooth, clean, level surface, and a little film cement applied to the scraped end of the blank. Film cement can be obtained readily and cheaply in small bottles complete with cap and brush. A bottle should always be kept to hand as it is often required, especially in joining up successive lengths of film; but if it should so happen that none is available at the moment, glacial acetic acid may be used with equal success, although it demands more careful handling. In an emergency alcohol constitutes a first-class cement, but it requires extreme care and skill because it is a solvent of the celluloid base.
After the cement has been applied to the cleaned end of the blank lead, the end of the unexposed coil of film is laid upon it, emulsion side uppermost, the overlap being about ¾ inch. Care must be exercised to see that the joint is made perfectly square and that the perforation holes of each piece of film come dead true, otherwise there will be trouble in passing the joint through the camera mechanism. When it has been superimposed satisfactorily, pressure must be applied to secure perfect adhesion. In order to ensure perfect jointing a film jointer should be used: in fact it is an indispensable and inexpensive tool.
When attaching the blank lead every precaution must be taken to protect the spool of unexposed film from light; only a very faint ruby glow should be used, for the cinematograph film is extremely sensitive. The cement dries rapidly, and the joint being found to be perfect the dark box should then be loaded. The coil of ribbon is slipped over the central bobbin. A hole large enough for this purpose is always left in the coil. The end of the lead is then passed through the velvet-faced slot near the bottom of the box. In order to prevent the loose end slipping back into the box, in which event there must be another journey to the dark room, it should be bent back and re-entered into the slot so as to form an external loop. The dark box is then closed, and securely locked, and is ready for insertion in the camera. It is advisable to carry at least two loaded boxes, especially if each is only of 100 or 200 feet capacity. The camera is provided with two dark boxes, one placed above the other. The upper box carries the unexposed film, while the lower receives the ribbon after exposure.