The dog movement, invented by Demeny, of France, and shown at C, has a disc G, centred at B, and carrying in a slot, so as to be adjustable, a semi-circular shaped pin A., which, on each revolution of the disc, comes into contact with the film P, drawing this down a distance of one picture space. The slack film is taken up by the continuously rotating sprocket-wheel D.
A diagrammatic view of the interior of a kine matograph camera is shown at D. The casing T is divided into three compartments : (I) A front compartment IT, containing a rotating shutter N, pin mechanism o P, and other parts not shown ; (2) a compartment v containing the film mechanism and magazines ; (3) and a compartment on the opposite side containing further mechanism communicating with the spools in the magazines, with the sprocket wheels and with the parts in the front com partment. The two magazines A B, consisting of light-tight boxes, fit into the back portion, and carry bobbins w x, on which the film is wound. This apparatus works as follows : The roll of unexposed film L passes out of a small aperture al at the corner of the top magazine A, round guide rollers C n, engages by its perforations with the sprocket-wheel r, to which it is kept in contact by the roller H, is looped up at and then takes a downward course through the guide groove made in the gate G ; it passes out at the bottom of the gate, where it forms a second loop Ha, and then passes between spring-roller i and sprocket wheel j, under the guide roller x, and enters at the bottom magazine B, where it is wound up on the bobbin x. The sprocket-wheels rotate continuously, drawing the film from the supply at r, and taking it up at m ; the motion of the film in the gate G., however, is intermittent. During the period of rest, a surplus loop of film forms at which is then pulled down through the gate by the action of the pin o engaging with the perforations. The whole mechanism is so arranged and geared together that, just as the film is stationary, an open sector of the rotating shutter N comes opposite the lens and film aperture at R. Likewise, just as the film is making its intermittent move downwards, an opaque sector of the shutter w comes opposite the lens, so that being thus under cover, it is saved from being fogged. Through the centre of the camera and opposite the lens, a long tube v extends, with a detachable cap at s. This tube forms the sight hole for purposes of inspecting the image upon the film prior to exposure. The gate G is a kind of hinged door with an aperture in it, and its function is to keep the film flat and vertical during exposure, and also to act as a channel or guide. After taking a subject, the operator presses a button, and in so doing punches a hole in the film, at a point just above the gate, this enabling him to determine where one subject ends and another begins.
Each individual photograph requires an exposure of from to of a second, the shorter the exposure the better, provided there is sufficient light to produce a well-exposed negative. The lens must give really excellent definition. A slight lack of sharpness caused by movement of the object during exposure will not seriously injure the effect, but the stationary surroundings repeated in the succes sive pictures must be sharp. Rapidity in the lens is also a matter of importance ; f/6 or thereabouts is sufficient for most purposes, and at times f/8 or even fir! can be used. The focal length will be short, so that the attendant defect of great rapidity, namely, lack of depth of definition, is not of great importance. The lens that is generally employed has a focal length varying from ij in. to 4 in.
The lens that has been employed for taking the photograph is frequently used for its pro jection upon the lantern screen ; this is a mistake, for a lens with the largest possible aperture, at least 1/4, and better f/3, of the Petzval form should be used for projection, unless the lens is of more than 4-in. focus, in
which case it is not of so much importance.
Projecting machines vary as regards type and method of translation of the film, but all of them work on the intermittent principle. The film is brought to a dead standstill sixteen times per second, whilst within the same space of time it is also moved forward in a vertical direction downwards sixteen times ; this movement is accomplished at the moments when the opaque sector of the rotary shutter is opposite the optical system. The essential parts of a kinemato graph projector are shown at E, the main support and the gearing mechanism being omitted. A and B are the two spools to carry the film before and after passing through the machine, the top one being the feed-spool and the bottom one the take-up spool. An upper and lower sprocket-wheel c and D engage with the perforations of the film F. The latter passes from A, between sprocket c and spring pressure rollers H G, forms a loop at j, passes through gate x, past the exposure aperture L, goes under the dog M, between sprocket-wheel D and pressure spring rollers H I, and finally to the take-up spool B. Sprockets c and n work in unison. A surplus loop of film is provided at j, as in the camera already described. The top spool A rotates by reason of the pull made on the film and is free to revolve accordingly. The lower spool B is turned continuously by a slip-belt, so that the film is tightly wound thereon, as it comes from the sprocket D ; the slip-belt compensates for the constantly increas ing size of the roll of film on B. The gate x has springs and pressure pads which hold the film steady after its downward motion ; and the channel through which it travels is recessed, contact only obtaining at the edges where the perforations are. The gate turns on hinges after the manner of a door, in order to facilitate insertion and threading of the film, being fastened by a catch and held by a spring. A revolving disc with open sector constitutes the shutter o, which is geared in such a manner that the open portion arrives opposite the exposure aperture and optical system just at that moment when the film is brought to rest. Finally, a safety drop shutter P is situated between the gate and condenser R, its rise and fall being controlled by the governor Q. The governor does not allow of the shutter rising till the mechanism is running at the rate of showing sixteen pictures per second,, at which speed it is safe to allow the emission of the lantern rays through the celluloid film. The objective lens for throwing the image upon the screen is at s, between the gate and the rotary shutter. The lantern situated immediately behind the condensing lenses R contains the necessary source of illumination, an electric arc-lamp, the carbon pencils v w of which create the arc at u, at which point also a crater forms exactly in a line with the centre or axis of the optical system ; or a limelight jet can be used.
The film is threaded through the projecting machine with the gelatine surface turned towards the condenser, and with the pictures inverted. If on projection it is found that the halves of two pictures appear on the screen, the pressure rollers H I are raised, and the film lifted forward till the sprocket teeth engage with two perforations in advance of = its previous position. Another way is to raise or lower the gate K by means of the pinion and rackwork provided for the purpose, but the picture is not then always exactly opposite the centre of the optical system. Equally important, in order to get the picture as steady and life-like as possible, is that the handle should be turned with the greatest regularity and at the rate of two revolutions per second. (See also " Kammatograph," " Kinemacolor," and other headings.)