The essential details of the three machines named above can be described briefly as follows: (1) A camera has a light-tight compartment within which a fresh strip of film passes and stops intermittently back of a lens that is focussed on a subject, a rotating shutter with an open and an opaque section makes the exposure. (When the strip of film is developed it is known as the negative.) (2) A printer pulls the negative, together with a fresh strip of film in contact with it, into place by an intermittent mechanism before a strong light. A rotating shutter flashes the light on and off. (The new piece of film, when it is developed and the pictures are brought out, is known as the positive.) (3) The projector moves the positive film by an intermittent mechanism between a light and a lens; a rotating shutter, with open and opaque sections, alternately shuts the light off and on. When the light rays are allowed to pass the pictures contained on the positive film are projected on the screen.
PRINCIPLES OF THE PROJECTOR AND THE MOTION-PICTURE CAMERA COMPARED.
It seems unnecessary, perhaps, in these days of the ubiquity of snap-shot cameras, and the fact that nearly every one becomes acquainted with their manipulation, to mention that a photographic negative records the light and shade of nature negatively, and that a positive print is one that gives a positive representation of such light and shade.
A NEGATIVE. A POSITIVE PRINT.
A motion-picture camera of the most approved pattern is an exceedingly complicated and finely adjusted instrument. Its principle of operation can be understood easily if it is remembered that it is practically a snap-shot camera with the addition of a mechanism that turns a revolving shutter and moves a length of film across the exposure field, holds it there for an interval while the photographic impression is made, and then moves it away to continue the process until the desired length of film has been taken. This movement, driven by a hand-crank, is the same as that of a projector—previously explained—namely, an intermittent one.
This is effected in a variety of ways. The method in many instruments is an alternate one of the going back and forth of a pair of claw-levers that during one such motion draw the film into place by engaging the claws into perforations on the margins of the film.
PLAN OF A MOTION-PICTURE CAMERA.