The Optical Magic Lantern Journal (July 1894)

120 The Optical Magic Lantern Journal and Photographic Enlarger. covered by a spring shutter, provided with a small roller fitted to its edge so as to prevent friction. Each exposure from the roll is marked off, for cutting at the time of development, and at the same time an automatic counter records the number of exposures made. The camera can be provided with anv suitable lens, and it may here be remarked that the firm supply an excellent R-R-lens of their own make; whilst the front carrying the lens may be raised or lowered to suit requirements. The illustration shows this instrument fitted with roll holder the front cover of which is drawn out ready for an exposure. The camera for 4 by 5 exposures measures 64 by 8 by 7 inches and is covered in Morocco. 1:0: -——_ How to Make the Most of Your Light. By Tue Doctor. UsxpOoUBTEDLY the easiest way to obtain the best results in lantern manipulation, as in other arts, is to use only the most perfect and powerful apparatus. There are, however, often serious objections, mostly of a financial nature, to this course, even where the operator has the selection of the instrument he is to work with ; while in many cases, as in schools or other institutions, he has to do the best he can with apparatus more or less ready to hand. To meet such cases it is proposed to review afew of the causes of poorness of illumination. It is hardly within the scope of this article to discuss the relative merits of blow-through or mixed jets, as it is presumed that the lanternist is already provided with one or the other. If, however, there is any opportunity for choice, the mixed jet is greatly to be preferred; not only on. account of its greater brilliancy, but also on the | score of economy of gas, and of the improved definition given by the smaller incandescent surface. The experience of many years has also conclusively shown that, particularly when compressed gases are used, it is quite as free from danger as the blow-through or so-called ‘‘ safety’ jet. Care should be taken, whichever form ig used, that the nozzle of the jet is perfectly clean and smooth. It will frequently be found that the aperture is partly blocked by pieces of lime or otber matter, and, in many cases, a corrosion will have ensued to an extent which seriously impairs the light-giving powers cf the jet. The remedy is of course simple and cbvious. A jeweller’s broach is a very useful tool for clearing and rounding the nipple of a mixed jet or the oxygen tube ofa blow-through. Not the slightest ‘‘burr’’ or roughness must be allowed to exist round these apertures, or a very pronounced hissing or singing noise will make itself apparent before the light has reached its maximum brilliancy. It may appear to be a work of supererogation to point out that the lenses, both condensers and objectives, should be scrupulously clean and bright, but the fact remains that they are not always so, even when being used by those who do know better. A very thin film of dust or smoke upon the objective will scatter so much light as to make the projected picture foggy in the shadows, and, by so doing, cause the high lights to look dull by comparison. It is a good plan to carry lenses and condensers in a separate partitioned box, and thus avoid the fine coating of lime dust, which they so frequently acquire when they travel as part of the lantern. Unless circumstances prevent it, the size of the projected picture should not be larger than the light at your command will illuminate brilliantly. The inexperienced operator does not realize the enormous gain in light to be obtained by showing, say, a l0ft. picture instead of a 12ft. one, and yet the difference in size is hardly noticeable by the general body of spectators, who will, however, appreciate a picture which they can see without possessing the catlike faculty of seeing in the dark. Where the lantern is worked from the centre of a room, and a certain number of the audience are necessarily behind it, a curtain or shield of some sort should be fixed to the back of the lantern body, so as to prevent the inevitable glare, mainly reflected from the condensers, from being seen outside. The writer has often seen this stray light so much in evidence as to cause a well-lighted disc to appear quite dust when viewed from the back of the room. The nature of the screen is of course an important factor in obtaining brilliancy. A whitewashed wall is an ideal screen, but is a little awkward to carry about, so that recourse has to be had to something a little more portable. The opaque screens made by Dyson and others answer well, but will only do for swall sizes unless in @ permanent position, as they must be rolled and not folded ; and this precludes their transportation by the ordinary lanternist. The best linen or cotton screen is, of course, the whitest and the thickest, as the thicker it is the more light is arrested and re flected. This is strikingly illustrated by the increased brilliancy of the light where it falls upon the seams in an ordinary sheet; these _ showing as much brighter lines where they