Dissolving effects in kinematograph pictures may be produced in two ways. If it is desired to make provision for such effects at the time of taking the original negative film, it is accom plished as follows : An iris-diaphragm, capable of completely closing at the centre, is fitted to the camera lens, and a short length of film is run through at the commencement whilst the iris is completely closed. Proceeding to wind through the film, the iris is gradually dilated and finally brought to its full aperture. The effect upon the sensitive emulsion is that the image of the object to be photographed fails to impress itself at first, and as the aperture enlarges in the iris, the film is more and more impressed, till at full aperture a full exposure is secured. The negative is then developed in the usual way. Such a negative will yield a positive in which the image gradually grows in strength, and as, at the commencement, no image will be seen, on projection the subject upon the screen will appear to develop out of thin air. If the image is intended to dissolve away and thus give place to a different subject, the iris on the camera is closed gradually whilst continuing to wind the film. Thus, a reverse effect will result
when the negative is printed. Any subject may be treated in a similar way at the printing stage by regulating the illuminant used whilst print ing. Thus, at the commencement, the light is kept very low, and as the films pass through the printer the illuminant is gradually turned full on till sufficient light is produced to secure normal exposure. Vet another method is to keep the illuminant at a uniform brilliancy and to regulate the exposure by modifying the speed at which the films are wound through the apparatus.
To make one kinematograph subject dissolve gradually into another, double printing is resorted to. At that point where the first print commences to weaken, through reduced expo sure, a second negative (of the second subject) is placed in contact and gradually printed up, till it reaches full vigour. Hence, instead of one subject dissolving away entirely before a second begins to make its appearance, the image of the second subject will make its appearance, weak at first, but gradually growing in strength and finally becoming of full vigour, and this whilst the preceding image melts away.