The history of three-color photography (1925)

644 History of Three-Color Photography a different negative for every theater, that did not possess a given throw, which is absurd commercially. Brewster also patented24 two special cameras with registering pins for two separate films at right angles to one another, so as to ensure accu Fig. 180. Brewster's U.S.P. 1,258,087 (Page 643). rate register of the positive films with their respective negative images. In these patents there is also claimed the possibility of using a doublewidth film instead of the two separate ones. Special spacings of the perforations in the usual margins and the use of circular perforations in the center of the dividing space between consecutive pictures are also shown. The Printing of Double-Coated Stock. — The usual method of making negatives for two-color work is, as will have been gathered, by alternate recurring color records, and to print these in series of all one color, one may use either a contact method or optical printing. In the former case one has to be very careful that the image on the one side does not penetrate through to the other. It is obvious also that there would have to be some special device by which the negative can be shifted two steps, while the positive film is shifted only one. Optical printing has also been resorted to, defining this as the production of an image on a sensitive surface from a matrix by the aid of a lens system. It is, therefore, differentiated from contact printing in which the sensitive surface is pressed into actual contact with the matrix. In this latter case there is a material image on a substantial support ; whereas in optical printing, there is a real but aerial image formed on the sensitive surface; the actual negative, or positive, image being separated by an air space from the sensitive medium.