We have already commented upon the difficulties of the instantaneous shutter as a means of representing rapidly moving objects, in that the results do not usually convey more than the idea of suddenly arrested motion. A snapshot of a stage in the Derby contest fails utterly in comparison with the old racing print. The former can include only one particular set of muscular contractions, while the latter conventionally represents the successive series of movements involved when horse and rider are straining their utmost to be first at the winning post. And the very perfection of the modern multispeed or focal plane shutter, by its sharp delineation of detail, is an element in destroying the artistic effect.

In short, the great fault of the snapshot instantaneous photograph is that it gives us a faithful record of say 1/500 sec., whereas the event, witnessed by the observers as one continuous whole, occupied several seconds before it was completed. A single snapshot is but a small fraction of the story. But if we can take a sufficient number of these snapshots at short intervals, and then present them one by one to the spectators, a fair impression can be conveyed of what actually took place. The cinematograph does more than this. It causes the series of records to blend into what is apparently one photograph, in which the characters move and perform their parts at approximately the same rate, and in the same manner, as in real life.

The Optical System

We need not dwell at great length on the mechanism of the cinematograph machine, which serves to project the pictures on the screen. The strip of film containing these pictures is drawn past the lens system of the projection lantern by a series of jerks, moving exactly one picture's length with each jerk. In the old Zoetrope, or "wheel of life," of our childhood, the pictures were viewed through a black cylinder pierced with slits at intervals: in the cinematograph a revolving shutter cuts off the light during the change of pictures, and so performs the same office as the perforated cylinder.

Persistence Of Vision

It is this well-known phenomenon that renders the "living pictures" possible. An image once formed on the retina of the eye is, so to speak, photographed there for the time being. Years ago this was demonstrated in the advertisements of a famous soap; we were invited to gaze for a few seconds at the huge red letters on the hoarding, and then to turn our eyes upwards to the sky, when it seemed as if the letters were printed there. The image remains on the retina for a length of time, ranging from 1/8 to 1/30 sec. So that if the pictures succeed each other at the rate of fifteen or twenty to the second, and the changing process occupies only a small fraction of the time, say 1/8 of the space of time during which each picture is visible, the successive pictures will be seen blended into one. Were they to be drawn at a continuous rate without the intervention of a shutter, the effect would be a mere blurring.

The Camera

A similar piece of mechanism must be included in the instrument used for producing the pictures, so that each photograph may be taken, and the film jerked on for the next exposure in exactly the same way as it will afterwards be projected upon the screen. Otherwise, the camera might be described as of box form, fixed focus, magazine pattern, containing two or more film slides, which may each hold from 180 to 600 feet of film, and may be changed in daylight for others as required. A great stimulus has been given to the manufacture of lenses of very large aperture for the purposes of the cinematograph, working at from f/3.5 to f/5.4, and with a very short focus, so that pictures are often taken successfully when the atmospheric conditions are far from happy. The shutter is usually of the fan focal plane variety, adjustable to different widths of slit, and some makers claim for their shutters that they will give, when necessary, exposures as short as 1/5000 sec. Most instruments are sighted by means of the view-finder. However, a recently introduced camera is fitted with the reflex system for focussing the image.

The camera is generally sent out to meet the needs of professional operators, with a lens of the shortest possible focus. Whenever the light is good, and other circumstances will allow of it, we always prefer a long-focus lens, say 5 or 6 in., and whenever a film taken under such conditions is shown on the screen, the greatly improved perspective and truthful representation of real life is very noticeable. Set pictures can nearly always be arranged so that the actors shall keep within the narrower angle included by the long-focus lens. In choosing a cinematograph camera, a pattern should be preferred which will readily permit of interchanging lenses of varying foci; also one in which the film boxes are conveniently placed. Another good point is a method of automatically marking off on the film any change of subject, or a place where the film can be divided if too long for development at full length. Most good instruments allow of the film being drawn backwards as well as forwards in the production of "Trick films."

Anybody with experience in hand-camera work can soon become familiar with the requirements of the cinematograph picture-producer. The only serious difficulty he will encounter is in turning the handle which actuates the changing mechanism at a uniform speed, and without any jerks or abrupt stoppages. Much practice at home with an empty camera is advisable, keeping an eye on the indicator dial, and timing it with a watch, till one unconsciously acquires a rhythmical motion of 15 to 25 pictures a second. The so-called "Trick films" are produced at a much slower rate, enabling the actors to perform feats which, when the film is run rapidly through the projection lantern, appear absolutely magical or ridiculous, as the case may be.