A comparatively recent contribution to the steadiness of the picture on the screen is the narrow, transparent violet vane placed on the shutter frame opposite the opaque sector. In spite of the brevity of the dark gap there was a certain letting down of brilliancy, noticeable to the eye toward the close of the dark gap which was emphasized when the light came on again in full force and these closely following con trasts proved very tiring to the sight.. The violet vane, by cutting into the high brilliancy, reduces the representation to a slightly lower but more uniform illumination. Other import ant accessories of the lantern are the heat screens, which stop a large proportion of the intense heat rays inherent in the condensed light from reaching the film and ifijuring the pictures. One ingenious device provides for the complete intercepting of the light and its contained heat unless the film is passing through the gate at a speed sufficient to protect it. Another closes this "fire shutter," as it is called, instantly in case the film breaks.
When all is said, however, the exhibition of moving pictures is simplicity itself as compared seem to vie one with another to thwart the design of the camera man.
The camera which has been designed to overcome all these external difficulties and many others peculiar to moving-picture work is a marvel of ingenious adaptation and me chanical skill.
Of supreme importance in the kinetograph camera is the lens, which is so designed as to admit the largest amount of light consistent with sharpness of definition and with the short est practicable focus. The factors of the lenses usually employed in taking moving pictures are for the focal length, 2 to 3 inches and for the with the intricacies of making them in the first place. The processes of photography in any case require for success an extreme nicety, of adjustment of many factors. It is a praise worthy feat to secure a single excellent "snap shot.* The task of the moving-picture photog rapher is to take thousands of pictures of such uniformity as to appear one continuous view, and of such excellence in definition and depth of focus as to be capable of magnification 10,000 times and still be satisfactorily sharp and clear. And all this is to be done often where the lighting is beyond control, where the only available position for the camera is one that no photographer would willingly choose, and where swarming crowds of bystanders working aperture f/3.8 to f/3.1. One promi nent lens house has produced a lens of 354-inch focus and a working aperture of f/1.9, with which have been made some very successful films under the most adverse conditions of lighting. It is not to be understood that the
lens is habitually used at its full aperture. This is the rule only in extreme cases of under lighting. The usual aperture employed in good light is f/16. Next in importance to the lens is the shutter which must be capable of adjust ment with the utmost nicety to control the length of time the light transmitted by the lens is to act on the sensitive film. The shutter makes one revolution for each picture taken. that is, ordinarily, one-sixteenth of a second.
The larger part of the disc of the shutter is opaque, one section being cut away to admit the light to the film as it passes the gate. This cut-away sector is adjustable in size of open ing, so that for quickly-moving subjects the actual time of exposure may be reduced to a very small fraction of a second. With moving pictures, however, extreme sharpness of the sub jects in motion is not a necessity, a slight blurring being rather an aid to the general optical illusion.
The interior of the camera otherwise re sembles in fittings the exhibition lantern, ex cept that everything about • it is in light-tight compartments. A large reel carries the sensi tive film before it is exposed and another takes it up afterward. The hook contrivance for moving the film at the gate and the arrange ment of sprocket wheels and idlers to keep it in motion are practically the same, and the entire mechanism is worked by the crank turned by the camera man. Fig. 2 shows the actuating mechanism which operates the film, without the gear-wheels which connect it with the driving crank. F, F, represent the film cases, the upper one full of new film. The sprocket wheels, S, S, turn so as to keep the film in loops with no strain on the hook H. L is the lens with the pivoted shutter behind it and T is the focusing tube. Other devices, however, are attached to the head of the heavy tripod which carries the camera while it is being operated. There is a gearing which swings the camera around slowly on a horizon tal plane, and so enables the camera man to make a panoramic view or to follow a moving subject with his lens. A finder at the side of the camera gives him continually the exact view which is being impressed upon his moving film. For a view which lies above or below the plane on which the camera is standing there is a tilting device by which the horizon of the pic ture is kept in a level position. Both of these movements are made by cranks at the left of the operator and turned with his left hand.