The Optical Magic Lantern Journal (March 1891)

The Optical Magic Lantern Journal and Photographic Enlarger. gI which ought to be fixed. This condensing lens should be of a form to suit the distance at which the objective is situated. For example: if it: were one of short focus, the focus of the condensing lens might be 8in. or thereabouts, to which end a plano-convex of sin. diameter and about ain, radius would suffice. If, however, to suit the requirements of a very long hall, an objective of much longer focus had to be employed, then | would the focus of the condensing lens be long in a corresponding degree; and as a planoconvex lens of that diameter would be thin and not cost very much, he suggested that the perfect lantern ought to be fitted with more than one of these. The focus of a plano-convex lens equals the diameter of its sphere of convexity ; thus, for a 16in. objective, the radius of the condensing lens would be about 8in., which, with sin.diameter, will give a practically thin lens. With regard to a possible objection—as to loss of light by reflection from two extra surfaces— that was altogether unworthy of consideration in view of the greater intensity and equality of light obtained by the triple system. The angle of light thus included is nearly ' gs deg. as against 60 deg. by the best commercial condensers. Mr. E. M. Nelson subsequently mentioned that the intensity of light at different distances from the condenser varied as the square of the sine of half the angle included, from which | the great gain obtained by this system recommended might be estimated. 30! The Lantern for Suffering Humanity. ‘WE are pleased to announce that our efforts for providing an occasional entertainment for patients in hospitals and kindred institutions have been so far successful. Several such movements have started in various parts of the provinces. Mr. Teale, president of Plainfield Camera Club, near New York, U.S.A., writes to say that he intends putting the movement on | foot there. For the use of Metropolitan institutions, the following donations have already been made :— Messrs. Perken, Son. and Rayment, 99, Hatton garden, EC., a bi-unial lantern with attach, ments for converting into two single lanterns. Mr. Walter Tyler, 48, Waterloo road, a helioscopic lantern, complete with blow-through jet. ‘Messrs. York and Son, 87, Lancaster-road, Notting-hill, 154 slides in sets. ‘Mr. R. H. Clark, Royston, Herts, (comic). J. W. and S., oxygen bottle and carriers. Mr. F. J. Balson, N. Allington, Bridport, 16 slides. Hon. Slingsby Bethel, 15 slides. 48 slides | | THERE are few but who associate the name i Walker Co., and Brins Oxygen Co. (per Mr. Murray) have promised to fill the bottles with oxygen as required, Messrs. J. F. Shew and Co., Newman-street, screen. Several who have promised slides have yet to be heard from. The committee have a list of volunteers who have kindly offered their services, anda programme is now being arranged. More slides and other sundries are yet required, and of course money in hand is necessary to cover the expenses of carriage of apparatus, &c. For this pur : pose it is intended to open a subscription list, which at a. J. 10 O present stands thus :— Mr. R.C. Ralph Hon. Sec. ... . si .. 10 0 Each donor, volunteer, or annual subscriber of 5s. and upwards will be considered a member of the Hospital Lantern Society, whilst all subscribers of ros. and upwards, will have the right of nominating | an institution in which they may be interested, such to | obtain priority. Several exhibitions have already been given at the London Hospital, Camberwell, Clapham. Communications to be sent to the hon. sec. and treasurer, J. J. Jones, 10, Lydon-road, Clapham, S.W.; or to J. Hay Taylor Editor of this Journal. Hand Cameras for Obtaining Slides for the Lantern. “Facile’... .. (Fallowfield)... ... see March Ist, 1890. No.1 “Giah" ... ... (Mawson & Son) .. 4. 5, May Ist, 4, 4) 2 ‘ Quadrane" ... (W. H. Humphries & Co.) ,, June Ist, 4, » 2 “Eclipse” . (J. F.Shew & Co.)... «5, July Ist. yy yy 4 {Eureka . (W.W. Rouch & Co.)... 5, Aug. Ist, ,, » a“ Key" .. 4. (Platinotype Co.) .. «4, Sept. Ist, 4, », 6 “Optimus” .... (Perken, Son & Rayment) ,, Oct. Ist, ,, » 7 “The Griffin" — (Griffin & Sons, Limited) ,, Nov. Ist, 5, » 5 ‘The Swindeu-Earp" Patent és ws 5) Dec. Ist, 4s », 9 Collins” (C. G. Collins) » Feb. Ist, 1891. No. 1o.—-KODAK. Kodak with hand camera, and the expression 40 /odahk (2.2., use a hand camera) is a familiar one. Fic. 1 The Kodak owes its origin to the Eastman is an extremely compact piece of apparatus. Although Kodaks are made in various sizes, from 2+in. circular pictures to 5in. x 7in., we will