The Optical Magic Lantern Journal (March 1892)

20 The Optioal Magio Lantern Journal and Photographio Enlarger. all more or less delighted with change, children of large growth as well as the youngsters, and so I say give it a trial ina thorough manner, and see if you do not please your friends. How often has it been said afttran entertainment given with first-class apparatus and slides, “ How very nice it all was. I had no idea a magic lantern could do anything like that. How ever did you produce those pretty effects ?”” Now let metry and show you how it is done. First of all, we must get our apparatus, as far as the stages are concerned, perfectly true. Our optical systems must be identical, and the lights must be capable of being raised or lowered at will, A moving lantern front and stage may be thoroughly well made, but it is almost a matter of impossibility to get it so true that it shall retain its position for vertical truth at all points of its inclination. At first we used to get the Stages true by trial or error, using a pair of ‘similar pictures in standard-size frames, and altering the fronts until we succeeded in getting them very nearly exact. Then we fitted a kind of rocking arrangement, and I remember, in one instance, a large amount was spent in workmen’s time and material, and a large expenditure of patience in getting atriple lantern correct. With these systems it did not follow that, if the registration was all right at one distance with a certain focus lens, it would be correct with another. It Was not until a customer insisted on what I call a pin’s-point registration that I thought of the present plan, and which was duly patented. A customer, after receiving his apparatus, which Was in every way up to the standard of that " time, said he could not register his effects pro perly. When asked him to point out any want of register, he took five ordinary pins, and placed one on each side of the foreground, two in the middle, and one on top of the picture. Then, when the second picture came on, it was seen the position was not the same, and if the slides were to be true enough to interchange from one stage to the other, no modification of the apparatus then known could make it so. Eventually I came to the conclusion that, as truth was wanted in both the vertical and horizontal planes, a system of adjustment must be adopted that could, when once found, be fixed, and so I had rising runners made with adjusting screws, having lock-nuts at each end, and a strong stop (Fig. 1), Fic, 1. also fitted with a lock-nut, for side of stage. Rising screws and registering stops had pre. viously been used, but a combination of same with stop and lock-nuts was not known. As it is necessary to have two standard slides to work to in setting the apparatus, similar crosses set in frames were resorted to, one line being vertical and the other horizontal, while letters in each quarter assisted for rectilinear correction. Even this exactness has been improved upon by Sir David Salomons (Fig. 2), who has been per Fic. 2. fecting the triple lantern for the past four years, and as he found the wooden frames liable to alter with dryness or moisture, and the film of the photographic cross an element of uncertainty, he had made—as an absolute standard to work from—mathematically divided registering slides so set from trued edges that the distances from the base and one side to the centre must always be the same. Although the first system is near enough for most purposes, yet for those who aim at absolute perfection, the latter is without doubt the system. In the case of the ordinary wooden-framed slides, the requisite centering has to be accomplished by placing strips of cardboard in the groove of the wcoden frames, until the picture is true to the eye. It is then placed in the lantern after the stage has been registered, and if it is found not to superimpose with the other slide, or slides, with which it is to register ; then the frame must be planed away truly until it doesso. With frames that have movements, such as panoramas, the registering must be done from stops fixed to the wooden frames to abut against the ends of runners. These runners must be exactly cut or filed, so that all are the same distance from the end to the optical centre of lantern. In Sir D. Salomons’ arrangement shown in Fig. 3, the exact distance can always be re-estab f ip ry { 1 oe eee oe one ee ee { Meducs 2 ¥ Fic, 3. lished—supposing for some purpose the side stop adjustment for ordinary framed slides has had to