The Optical Magic Lantern Journal (November 1901)

84 The Optical Magic Lantern Journal and Photographic Enlarger. 8 inch focus one working at //3:16 gives more | light on the screen. A portrait lens with the aperture //4 of the Voigtlinder symmetrical type gave the most pleasing results with very satisfactory definition. A collinear lens with the aperture 7/54 gave extremely sharp defivition, but strange to say the definition is made almost painfully sharp, and therefore there is an | absence of brilliancy on the screen, even though the light passed could be considered sufiicient. If we next compare 20-inch focus lenses of the different types the case is very much altered. The rapid portrait type will give no more illumination on the screen than the Euryscope type working at //6-3; in fact, a favourite lens for projecting at a long distance is a 20-inch | This always gave — focus, one working at //S. me ample illumination and very satisfactory definition. T have found uo disadvantage in the absence | of bellows between the carrier support and the | projection lens. Inasmall room it is easy to fix a cloth to exclude stray light. I have tried a number of limelight jets. For use in ordinary rooms with screens up to 10 feet diameter, the jet I have found most efficient is Wrench’s Injector. It gives a good light without the necessity of using two cylinders. As the electric arc light has more white or blue than limelight, slides made for use with the latter lose some of their effect when shown with the are light. To remedy this I would suggest placing a light yellow screen between the condenser and the slide when the latter light is being used. In conclusion, a number of slides were pro| jected upon the screen in order to show the © Several | members asked questions relative to the instru| results obtained by various lenses. ment before them, and to these Mr. Baugh replied to the following effect:—The diameter of the condenser should be at least 41 inches, as it should be more than enough to cover the slide, so as to permit of slight focusing by adjusting the upright carrying the slide. To obtain the very best results, it was necessary to adjust the light after changing from one lens to | another; but in this instance he had not done | so, aS his intention had been to show their power of illumination at different apertures, rather than their power of definition. ‘Io carry out a satisfactory test for definition, it was necessary to have everything absolutely cen| tered ; the light must be carefully centered, right distance from the condenser. | the fixed glass. TuEovore — BRown =¢ fie r; i Sd EE A BARROW ; ON THE TIGHT ROP¢ . PAR ide Sac ai rope furnishes a splendid subject for a mechanical silhouette slide, whilst the effect produced upon the screen is not surpassed by any of the slides described’in this series. In the first place, I employ the ordinary framework, which is so well known by all lanternists that a description of it would be superfluous. Let it suffice to _ say that it is fitted with one fixed glass, and | has a groove in which slides a longer glass. In Fig. IV. a indicates the position of the wooden framework, whilst in the sectional view, Fig. III., a is the fixed glass and F the movable one. As the manner of fittiog up the fixed glass is by far the more important, I will deal with it first. Speaking generally, it holds the man and the wheelbarrow. To particularise, the head and body of the | representative of the man is cut out of thin fretlenses accurately focused, with the slide at the ° wood and glued to the front (or interior) side of This portion is shown black in