Illustrated Catalogue Of Magic Lanterns (after November 1889, probably 1890)

MCINTOSH BATTERY AND OPTICAL CO., CHICAGO, ILL., U. S. A. 8(j pass outside of it and are lost; when the light is too near, as at N, the rays do not fully illuminate the image. Ihe Size of Disk. — The size of the illuminated circle on the screen, with a given lens, depends upon its distance from the screen. In Pig. Or the arrow A is shown of a certain size on the screen, its length is equal to the diameter of the cone of light at that point. If the screen be moved nearer, as at B, the cone of light is inter- cepted at a point where the diameter is less, therefore the image will be smaller. If the screen be removed to E , where the rays have widely diverged, the image will be correspondingly enlarged. The rays of light nearer the lens being more condensed, a brighter image will be shown at B than at E, where they are diffused over a larger surface. The shorter the distance between the lens and the screen, the smaller and brighter the image; the greater the distance between the lens and the screen the larger and less bright the image. The dis- tance can be considerably varied without impairing the imao-e on the screen when sunlight, the electric light, or the lime-light are em- ployed, but with an oil light it is practically impossible to produce a satisfactory picture of more than ten feet in diameter. Inversion of Image. It is necessary to invert the slides as they are placed in the focus of the Lantern Lens for a reason which will be apparent on examination of Fig. G. Since the rays of light come to a focus, and cross at a certain distance from a lens, it follows that the rays from the upper part of the object, near the condenser, will be thrown on the lower margin of the screen, and vice versa, giving an inverted image of the object. To make this image appear right side up to the audience, the slide must be wrong side up in the lantern. r To Focus Image on Screen. —Tiie milled head screw on the Stereopticon Lens is to be turned until the image comes out distinct and sharply defined upon the screen. If this screw is turned as much as possible without bringing out the image clearly, it wil be neces- sary to lengthen or shorten the sliding tube which holds the lens A little practice will enable the operator to adjust the focus instantly. To Show the Slides.—As photographic transparencies from dif- ferent manufacturers vary somewhat in size, the Slide Carriers fur- nished with the McIntosh Lanterns are adjustable for different sizes. The transparencies show to better advantage when they are correctly placed before the condenser. Each new lot should be examined and marked by a slip of paper pasted across one corner, to indicate which is the front side. To Light the Sunlight Lamp.— Use only the best grade of coal oil, not less than i 5 o° test. Elaine is preferable when it can be obtained. Twelve fluid ounces of oil is sufficient for a two hours exhibition, and no more should be poured into the lamp, as it is neces- sary to leave about half an inch unfilled, so that the lantern front may be raised without spilling the oil.' Place the lamp in the lantern, take off the reflector and raise the hinged glass to light the wicks. The wicks must be evenly trimmed, and turned very low when first lighted ; in a second or two very slowly raise each wick a little at a° time,