The Optical Magic Lantern Journal (January 1899)

_ ‘The Optical Magic Lantern Journal and Photographic Enlarger. HE principle of the roller curtain effect, although simple enough to experienced lanternists, seems to be somewhat of a mystery to the tyro. As the ranks of lanternists are continually being recruited from the latter, and as we have quite lately received several letters bearing upon this subject from beginners, we will hark back to the subject go as to make the principle understood. Several of the letters spoken of are evidently from those who possess a single lantern. One letter before us says: ‘‘To bring an opaque curtain over a picture on the screen is easy enough by interposing close to the picture a sheet of anything that is opaque, but to bring a coloured curtain over a picture without showing the picture itself seems to be somewhat of a mystery. I lately saw such done and there was not seen through the coloured curtain the slightest trace of any portions of the picture itself. Why was this and how was it done ?’”’ With a single lantern it is simple enough to bring an opaque curtain or shutter over a picture by sliding up over the picture from below athin sheet of any opaque material, a convenient carrier for this purpose being some time ago devised by Mr. Davenport, the secretary to the Society of Arts, and is sold by Mr. J. H. Steward, of the Strand. To give the effect asked about with a single lantern is impossible for the simple reason that if a transparent or coloured curtain slide were so used the picture itself would appear on the screen at one and the same time, much after the same style of placing two pictures one in front of the other in the lantern stage. To obtain the effect of a coloured curtain rolling down over a picture it is necessary that two lanterns be employed. Let both discs coincide upon the screen, and in the stage of one place a view and in the other stage a curtain slide. If both illuminants in the lanterns are up, a blurred mass consisting of picture and curtain will be seen, but if one lantern be shut off, the picture from the other will appear plainly. If a piece of cardboard be placed immediately in front of the curtain slide so as to exclude the light from passing through, say one half of this slide, so will just the covered portion be cut off from the screen, allowing the space of the same size occupied by the other picture to be seen distinctly, whereas the remaining portions will consist of the blurred mass of part curtain and part picture. If now in front of the view slide in the other lantern a piece of cardboard be slipped at the opposite side of the lantern to that which was placed in front of the curtain slide, a corresponding portion of the picture will be shut off the screen, and we have one half of the projected disc containing a picture and the other half the curtain. By slightly adjusting the pieces of cardboard it will be apparent that each picture can be exactly cut off in equal portions. Supposing it possible to slide the two cards along at exactly the same rate—tbe one to cover more of the picture, and the other to reveal more of the curtain slide—it will be evident that the curtain slide will appear to be unrolled sideways over the picture. Such, then, is the principle; but in practice this covering and uncovering takes place at the top of one slide and the bottom of the other. With bi-unial lanterns all that is necessary is to make a metal strip sufficiently wide to cover the stage opening, and to make it to slide up and down close to the pictures. The length of this strip must be such that it will cut off one end of the one slide at the same time that the other ends of the strip is uncovering and revealing the other picture, the edges of the strip being so cut that only a fine line of demarcation is seen on the screen dividing the two pictures. By means of a roller curtain so fitted many pleasant changes can be obtained by giving the appearance of one picture rolling up or down over the other. Flash Light Dangers. By EDSAR CLIFTON. in aur magnesium flash light is no % longer ‘the toy of the novice ; it has become a recognised factor in the every-day practice of the skilled photographer, and a few words of <2) caution as to the methods to be followed ge in handling the lamps and powders now v’ commonly used may not be unseasonable. Under the generic term of flash light are classed the light produced by blowing or otherwise projecting powdered magnesium through a spirit or gas flame, that produced by the ignition of an explosive compound such as magnesium and chlorate of potash, and that obtained by igniting sheets of paper or similar material carrying in their substance the necessary oxygen-giving salt and coated on the