The Optical Magic Lantern Journal (August 1892)

The Optical Magic Lantern Journal and Photographic Enlarger. 91 that might be tolerated to seven feet, and perhaps more, but after seven or eight feet the blowthrough limelight becomes necessary, and this may be used up to ten or even twelve feet, and after that the mixed jet, with oxygen and hydrogen under pressure, is indispensable. Ether may be used in place of hydrogen or coal gas, but I sce no advantage in its use in any way. The oil-lamp, then, as I have stated, is only suitable up to six feet screens, and the question comes now, is six feet large enough? The answer to that is, it depends where it is to be used and the size of the audience. I have given a good deal of pleasure to private friends at home by even a less picture, but in a private drawing-room or a dining-room it is not always convenient to fix a six-feet screen, and very often when it is convenient there is either a fire burning in the room or some abominable reflections, that cause a good deal of trouble by interfering considerably with the results. All these objections are dispensed with by using a transparent screcn such as I now introduce. In this little waterproof case, not unlike an wnbrella-cover, except that it is a little longer, is a roll of a particular kind of semi-transparent paper three feet eight inches wide. The outer end of it is attached by six drawing pins to a wooden lath five-eighths of an inch square, having suitable fittings for attaching to two light stands, also contained in the waterproof case. The screen, as you will see, can be erected on one end of a dining-room table in threc minutes; and, if the table is long enough the lantern can be placed at the other end. The audience sit in front, and I think you will be surprised to see how beautiful pictures look when projected in this way. The reflections from the house-fire do not interfere with the results in the, slightest degree. We may even permit a tolerable light in the room, and you may strike a match to light your cigar without impairing the brilliancy of the picture. And, now that all is ready, you see a beautifully illuminated picture three feet six inches square by a sciopticon, and which I maintain is large enough for most private-house exhibitions, or even in a small schoolroom, where the audience is not too large. I am not advocating small screens in preference to large ones, for all depends upon circumstances; but I do prefer a well-lighted small screen to a large one with inferior illumination, and especially so when we can get to the best position from which to view the pictures ; and here another matter may be of interest. The lanternist inquires what is the most suitable sized screen for a certain size room? and the audience ask which are the best seats to sce the picture from ? To say that the screen ought to be in proportion to the size of the room is the general way of putting it, and to sit about the middle of the room is the usual reply to the best position, Now, it is an established fact, which was recently demonstrated at the Stereoscopic Club, that the most correct position from which to view any photograph is at the angle at which the photograph was taken. Thus, if we make a picture by a twelve-inch lens, and we wish tc appreciate size and perspective correctly, we must view the picture at twelve inches from the eye. Tocxaniine it at a nearer distance is ecual to it being taken by a longer-focus lens than twelve inches ; and to see it at a greater distance gives the impressions of one taken by a shorterfocus lens. Then, if we make quarter-plate negatives by a five-inch lens, to see it correctly we must either use a magnifying-glass or a stereoscope, or we may magnify it by the lantern ; but the principle is just the same. If we make lantern slides by contact from quarterplate negatives taken by five-inch lenses, and mask these down to 2: inches, as is usual, and then project these slides to 6 feet, we have a magnification of 296 diameters; then 26 by 5 (focus of fens) gives 11 feet. If we project the slide to 12 feet, or about 52 diameters, this, multiplied by 5, will show us that, at 22 feet, we should see the pictures at their best ; and, from what has now been said, it will be understood how incorrect it is to make lantern slides which are to be shown in series from negatives taken by lenses of different foci, or what comes to the same thing, is making contact slides from quarter-plate negatives and other contact slides from portions of whole-plate and even larger negatives. At a lantern exhibition, not very long ago, a series of slides of Haddon Hall were shown. The photographer had used a nine-inch focus lens for most of the exterior views, but for all the interiors a five-inch lens was used. I well remember the view from the terrace steps, showing the main front of the building, with the ball-room windows ; and the next view was the interior of the ball-room. It looked so very large, that no person in the world who did not know the architecture could have imagined a room of such dimensions to be contained in the building we had just seen upon the screen. It was as ridiculous as for an architect, to submit unfigured plans of the rooms in a house all drawn to different scales, to fill up the paper, and where the bath-room and the w.c. might be shown the same size as the dining-room, no true idea could be formed from such drawings or such photographs.