Moving Picture World (Sep 1916)

1832 """ Miiiiiiiimiiinii jjj.iiiMji I.L-— .. ^rrTTmrrrT-TFilllllllliiiw THE MOVING PICTURE WORLD September 16, 1916 "millllMllimmuli"— ^ Motion Picture Photography Conducted by CARL LOUIS GREGORY, F. R. P. S. Inquiries. QUESTIONS in cinematography addressed to this department will receive carbon copy in the department's reply by mail when four cents in stamps are inclosed. Special replies by mail on matters which cannot be replied to in this department, $1. Manufacturers' Notice. It is an established rule of this department that no apparatus or other goods will be endorsed or recommended editorially until the excellence of such articles has been demonstrated to its editor. The Future of Motion Photography As a Profession (Continued). Films will be made to fit certain courses of instruction by competent educators who will pursue well thought-out courses laid out in logical sequence along scientifically formulated lines. Such pictures will take up a subject from its beginning, pursuing all of its phases in the same manner that a text-book does at present, so that the student will have demonstrated before his eyes in a comprehensive manner the same things which he to-day digs out with repugnance from the dry-as-dust leaves of his dog-eared school books. Even to-day with the enormous magnitude of the industry there are still many croakers and knockers who are ready to tell you that the motion picture has reached the crest of its popularity — that the public is becoming satiated, and that from now on will come the decline. They are all mistaken. Enormous as the business is — the fifth in importance in this country — it is still moving onward and upward. Rome was not built in a day, and with all its rapidity, the motion picture industry will not be revolutionized in an hour. Many of these things of which I have spoken may be a long ways in the dim future, but they, or some more magnificent manifestation which I am not able to perceive, are coming as surely as the sun rises in the east. And the worker who keeps his face to the east, and with unfaltering effort keeps abreast of the inevitable progress, must eventually reap his rich reward. The Use of Color Filters in Cinematography. The speed at which motion pictures are usually photographed is so great that the use of color filters is greatly restricted. In still photography, many beautiful effects may be recorded with the longer exposure that may be employed. These are not attainable to the cinematographer because the speed at which he must work does not permit him to get enough exposure to impress his film. In consequence, very little attention has been paid to the subject by the manufacturers of film or by the cinematographer himself. There is, however, within a much smaller range than in still photography, a region where we may obtain results with color filters in cinematography and greatly benefit thereby. While the film ordinarily used in making negatives is not highly isochromatic, it is nevertheless somewhat sensitive to the yellow rays in the spectrum ; and if we employ filters which will not be too deep in color so as to bring the exposure beyund the limit set by the motion camera, we are able to produce many pleasing effects. There has been a great deal of literature written about the advantages of orthochromatic pictures although most of it has been in reference to still pictures. Ordinarily, the slight difference between the black and white picture which registers the image in values of blue light reflected from the object is not distinguishable to the ordinary untrained eye from that which registers in a scale comparable to what is termed "visual luminousity." This term is perhaps one which needs explanation. To the eye, the brightest color in the spectrum is yellow — but to the photographic print, blue is the lightest; consequently, when we photograph an object in which blue and yellow occur, the photograph will show the yellow as being very dark and tho blue as very light — whereas to the human eye, the brilliance is reversed. Isochromatic plates and films are those in which the sensitiveness of tho emulsion to yellow light has been increased by the use of a dye which lias tho property of making the emulsion more sensitive to the lower range of the spectrum. This dye does not, however, reduce the bluo sensitiveness to any great extent, nor does it increase the yellow sensitiveness enough to make the ratio of color brightness the samp as it is to tho human eye. Tho color filter is a transparent substance either of colored glass or a combination of glass and colored gelatine, which absorbs certain colored rays of light and permits others to pass. A yellow filter, fcr Instance, allows yellow lif;lit to paws through unobstructed. If it is of a light hue, it permits other colors to pass through also, but absorbs a largo percentage of the other colors. On the other hand. •Copyright, 1916, by the Chalmers Publishing Co. if the color is deep, it absorbs that much greater, until at last we reach a point where all of the other colors except yellow are absorbed. It is possible to prepare a filter which will absorb just enough of the blue light so that the action on the film is in the same ratio as the brilliance of the different colors to the human eye. This color, however, must be regulated so as to correspond with the sensitiveness of the emulsion to different colors. For instance, if we use an ordinary emulsion — one which is not of the order termed orthochromatic — we cannot obtain a record comparable to that of vision because such an emulsion is only sensitive to blue light. On the other hand, if we use an orthochromatic emulsion which has considerable sensitiveness to the yellow rays, we attain a very close approximation to visual luminosity. It may be well to state here that even the ordinary emulsion is faintly sensitive to the entire range of the visible spectrum and also far into the ultra violet — the region beyond the violet end of the spectrum which is invisible to the human eye. This faint sensitiveness, however, is so small in comparison to the sensitiveness of the violet end that the ordinary emulsion is quite useless in obtaining orthochromatic effects, and this very slight sensitiveness may therefore bs disregarded in any discussion relating to practical picture taking. A great deal of nonsense has been written in regard to the care which must be taken in excluding or cutting out the ultra violet rays in orthochromatic photography. Most writers on the subject fail to take into account the fact that although ultra violet rays are the most actinic (that is, have the most action upon the ordinary photograph emulsion) they are almost always entirely absent under ordinary conditions. In the first place, the atmosphere is highly absorbent for the ultra violet rays and at sea level and ordinary altitudes, they are comparatively weak — although still strong enough to produce considerable effect on the emulsion if it were not for the fact that the glass used in making lenses is practically opaque to these rays. We will therefore dismiss them from further consideration. It is not necessary that we go far into the laws governing color ; it is sufficient to state that all white light is simply composed of three primary colors, i. e., red, yellow and blue. Color is simply caused by the blocking out of one or the other of these primaries in various proportions depending upon the hue. It is far better and very much cheaper in the end to buy filteralready prepared by competent makers than to use valuable time experimenting in the making of your own — the shortage of adequate dyes alone presenting at this time an almost insurmountable barrier. The subject of the making of color filters is too long to be taken up here, although persons who may be interested in experimenting along these lines can find enough material in various text books on color to give them an endless variety to work upon. It is also quite possible for workers to color-sensitize their own films ; but almost superfluous at the present time to give directions for color sensitization, as it is practically impossible to obtain the proper dyes at any price. Should there be any readers of the present article interested in the subject, the writer will be glad to furnish the names of the best text books on the subject — with the warning that the price of the best dyes for color sensitization of photographic emulsion is at present over $G00 an ounce. The introduction of a color filter into the path of a light beam lengthens the necessary exposure simply by reason of the fact that the filter has absorbed or filtered out some of the rays which would otherwise have acted on the film. The percentage of light held back depends, of course, upon the absorption of the filter used. It is plain, therefore, that not only will the exposure time be increased when the filter is used, but that the increase will vary according to the type of filter and the sensitiveness of the film used. The number of times that the exposure is increased over that required for the same object without the use of the color screen is called tne multiplying factor of the filter. Since the filter invariably increases the exposure required, it becomes apparent that there are only a few filters which we can use in making motion pictures. The question now arises "When and where should we use a filter?' Since the filter increases the exposure so greatly, we are limited to subjects which are strongly lighted. Exterior pictures in the sunlight are about the only ones which come within the limited range. They are fortunately tho ones in which the filter may be used to the greatest advantage. In ordinary scenes out of doors where clouds in the sky add immensely to the beauty of the scene, it is seldom possible to render tho difference between the white of the clouds and the bright blue light of the sky without under-exposing the other objects in the picture. If, however, we hold back the blue light ot the former, using a light yellow filter, we can fully expose the objects in the foreground Which normally reflect a large percentage of tho yellow 1 ip.ht and at the same time retard the blue light of the sky — and thereby obtain a harmonious rendering and at the same time show the fleecy contour of the clouds. t7'o be continued)