The Optical Magic Lantern Journal (September 1890)

28 The Optical Magio Lantern Journal and Photographic Enlarger. Hand Cameras for Obtaining Slides for the Lantern. No. 5.—“THE KEY.” ONE of the features of the Key camera of which the Piatinotype Company are the proprietors, is its extreme simplicity, coupled with efficiency, and in describing its working parts a few words will suffice. The camera will be readily understocd fiom tle annexed cut, and the following remarks. The plates are contained in light metal double carriers, which are secured in place by simply pressing the spring clips seen at the side of the instrument. The carrier thus placed is then hinged up as seen in the dotted lines ; by this movement two operations take place automatically—a light-tight trap in the carrier opens and the plate is received in the focussing plane. Provision is made, in the event of an extra thin plate, whereby a spring can press it up to focus. and this can be used or not according to circumstances ; however, a quarter turn ‘of a small knob suffices to bring the spring into action. After exposure, the camera is reversed, and the plate zguin enters the carrier. The dark slides are extremely light, and pack together so closely that several may be placed in one's pocket. The lenses are rectilinears of first quality. The shutter works between the lenses, and can be regulated froma fraction of a second to 60 seconds, and actsasa diaphragm during the opening and closing. The front combination ofthe lens slides out to permit of the use of any desired stop being employed. The release for the shutter is a small knob, which is sunk to the level of the outside of the camera. By the aid of a milled head, which projects just sufficiently for the finger to operate, the lens may be focussed for varied distances, according to a graduated scale at the side of the shutter release. The camera is light and unobtrusive, 1s provided with a handle for carrying, and is finished in dead black mahogany, with a series of cross hatchings which give it the appearance of being covered with leather, without the disadvantage that leather after it becomes worn begins to fray at the junctions. This, however. is obviated by the manner in which the key camera is finished. | ment, and a little extra procedure. a Transparencies at One Operation. IN making a transparency ona gelatine plate, according to the mode at present followed, two distinct operations are necessary. The negative has first of allto be obtained, and then the transparency produced from it by exposure in contact and development. I will endeavour to describe a suggested method that would enable us to dispense with the second operation and the second plate. By such a method lantern slides couid be produced direct in the camera, while transparencies of any size could also be similarly obtained, duplicated, and multiplied. Suppose we intend to photograph landscapes, architecture, or, indeed, any kind of subject suitable for projection on the screen, there need not to my mind be much difficulty about the lantern slide being taken direct in the camera. The subject is the positive. A positive can be obtained from it by exposure, developLantern plates which are, I believe, usually coated with bromo-iodide emulsion averaging about 14 deg. sensitiveness on Warnerke’s sensitometer, can, of course, be exposed in an ordinary camera by employing inner frames. Imagine the exposure made and development completed. We have gota negative and desire a positive. First, well wash the picture and apply a very dilute clearing solution of hydrochloric acid and alum. When this has been thoroughly removed flood the (unfixed) negative with a solution of potassium bichromate and hydrochloric acid, as recommended on page 19 of this volume for use in the toning of transparencies. The developed negative soon whitens, becoming changed to silver chloride. When the bleaching action has gone to its uttermost, remove the solution and well wash the plate. Now, if the chlorised picture be entirely removed there will remain, wherever the light and the developer have failed to penetrate, a layer of unaltered haloid, perfectly gradated, which, if exposed for a few seconds to the light of the dark-room lantern, and then treated with the developer, will yield a positive picture. Ammonia liquor “880, diluted with about thrice its own bulk of water, and repeatedly applied, will quite dissolve off the silver chloride; a saturated solution of ammonium chloride used in excess has also been recommended. It is a weaker and slower solvent than NHs, and therefore must be used freely and given plenty of time. Theoretically, when the halogenized negative has been dissolved away, and the positive impression developed up, there should not be left in the film any portion of unaltered haloid, but as minute traces may possibly remain, it will be advisable to give the plate a brief immersion in hyposulphite. The niceties of exposure and development required will, of course, suggest themselves, and must be effected with great skill in order to ensure good results. For hand camera work the method suggested would, I fear, be a case of counting the chickens before they are hatched. Apart from the fact that such pictures are not always suitable for lantern illustration there.is such an interesting element of uncertainty about the important preliminary of exposure that it would be wise to ascertain if a negative had been secured before thinking about the positive. Wa. D. GREEN.