The Optical Magic Lantern Journal (December 1890)

C4 The Opticel Magic Lantern Jou placed on its stage is seen sharply defined, it follows that the sharpest image is in the same plane as the | surface of the ground-glass. When the focus is ob. _ tained the focussing screen must be removed, and the sensitive plate placed in its stead. It will be as well to mention that the actinic and visual foci of microscopic objectives do not of necessity lie in the same plane, in fact as a rule the actinic focus is slightly beyond the visual. In the low powers ; this difference is sometimes considerable, and in the . high powers so small that it may beentirely neglected. In consequence of this over correction of the objective, | on developing the plate, the image, which was accurately in visual focus. will be slightly indistinct, but as this error is constant, it may be very easily corrected in the following manner. Place on the stage of the microscope an object having a slight thickness, and focus accurately any part of it, preferably near the centre. Expose and develop a plate, and in so doing be very carefi/ not to alter the adjustments of the microscope or to shift the object on its stage. Now carefully examine the negative and note the part which is in sharpest focus, then having replaced the focussing screen, rotate the milled head of the fine adjustment until the sharpest part of the image seen corresponds with that of the negative. Makea careful note of the amount of rotation required to effect this, as this will be the correction that must always be made | (with the objective in use) after focussing, and of course before exposing. With many objectives no correction is required. If the negatives are for making lantern slides from I would advise that the exposure be very full, so as to obtain a negative soft and full of detail. Use the /owest power objective that will give the ne€cessary detail, and enlarge the resulting negative if necessary. One other point in conclusion—test screen and double back. and make quite sure that the ground glass and the sensitive plate are exactly In the same plane when in the camera. This is most important in micro work. * your focussing 10: Tr South London Photographic Society held an exhibition (members’ work), lantern entertainment and concert at Manover Hall, Peckham Rye, on the evenings of the 21st and 22nd ult. A fine display of work was exhibited. The judges, Messrs. Dresser, Trail] Taylor, and Warnerke, awarded the prizes as follows :—(A) Best general work, Mr. Rice, silver medal; Mr. Kkirby, bronze medal. (8B) Six best pictures taken at society's excursions, Mr. Kelly, silver medal: Mr. Farmer, bronze medal. (c) Best six local views, Mr. Webb, bronze medal. Inclass p, hest series of lantern slides, the merits were as follows: first, Mr. Rice; second, Mr. Farmer ; third, Mr. Boydell ; but it having been previously arranged that an exhibitor taking one medal was disqualified for taking another, and as Messts. Rice and Farmer had alreacly won them in Classes A and B respectively, the bronze medal was awarded to Mr. Boydell. The hall was well filled by an appreciative audience. Mr. Banks placed his fine triple lantern at the service of the society, and, with the assistance of Mr, Gardner, operated the instrument. Besides pictures, some apparatus was exhibited, including the 12 by 10 camera which the society lends to its members ; Mr. Howell had a stand of general apparatus ; and Mr. Slater, of Southampton-street, Camberwell, exhibited a quantity of styles of frames and mounts. Mr. Ranson's new hand camera and his roal and Photographic Bularger. Chromo-Litho Slides. By ALBERT TRANTER. BEING the possessor of one of those entertaining , instruments, a standard size optical lantern, I recently | purchased a set of 3}in. chromo-litho slides to use with it,and since their purchase the thought has struck me that pictures for the lantern could be so produced in a superior style if they were printed on glass coated ‘with albumen, in the same way as the glass plates are prepared to produce those beautiful albumen lantern photographs. ‘The advantage to be so obtained lying in the albumen presenting a somewhat absorbent character compared with the surface of the mere glass, and thereby allowing the outlines of the pictures to be presented in a less blurred or rough manner, sharp‘ness or clearness of outline being such an important Consideration when one’s credit as even an amateur lanternist is at stake. If such slides were carefully prepared, | think that for itlustrating subjects that are most likely to be wanted to be illustrated by the owner of a three or four wick lantern, they would answer most requirements of such a lanternist. Of course for producing views of natural scenery, such pictures will never come up to photographs, with all the details and lights and shadows which they give so accurately ; though to properly show those the ; lime or electric light is required. a * Since writing the above { have read the interesting item in the November issue -of this journal by Mr. Arthur E. Morton, reprinting on gelatine films by aid of the typewriter, and the thought has occurred to me that the same mode of printing, as regards the ; medium for receiving the impressions, could be adopted in producing the coloured chromo litho slides above mentioned, as I should think such or a ; similar surface to that described by Mr. Morton would be admirably adapted for receiving impressions made in producing such pictures ; the pictures afterwards receiving a coat of varnish to perfect their transparency before being placed between the two glasses. And I do not see why slides prepared in such a way could not be soldat the rate of, say, 3s.6d. per doz., for instead of printing on paper, and then having to go to the trouble of transferring them toglass, it would only be necessary to print at once on the gelatine films, and then varnish and mount same; instead of the tedious process of of having to use several sorts of varnish, and exercising no little care in removing the paper on which the pictures are printed. 10: An Effective Intermediate Regulator. ROARING or hissing of gas jets is an annoyance to be avoided when at all possible. and to obtain the maximum light with silence is the aim of lanternists. It has been said that a properly-constructed jet will act in a silent manner under a pressure of gas; but to ensure silence, the relation of the supply of compressed gas must be regulated according to the construction of the Jet, and in order to obtain the best light it is essential cap for studio use also came in for a large share of attention. that the regulation of the supply must be under