The Optical Magic Lantern Journal (November 1889)

The Optical Magio Lantern Journal and Photographio Enlargor. Mr. WALTER GRIFFITHS, Birmingham, has sent us one of his lantern slide-making cameras. This camera is intended for making slides from half-plate negatives, and it answers admirably. All that is necessary is to insert a negative at one end, a sensitised plate at the other, close the sensitive plate end, and expose the instrument to the light. No focussing is required. As a means of making lantern slides it is simplicity itself, and is sold at a very moderate price. +4 Correspondence. CANDLE POWER. [Lo the kditor. } S1R,—In the last number of your Journal there is an article on the ‘‘ Candle Power of a Light,” on which I beg to make one or two remarks. A “candle power” is said to be that of a standard candle, but its value is not stated, viz.,a sperm candle of six to a pound, burning at the rate of 120 grains per hour. Inaccurate photometric experiments the rate of consumption is ascertained by weighing the candle during the experiment, and if it be more or less than 120 grains per hour, the value of the light is increased or diminished accordingly. In speaking of a deeper shadow being cast by a stronger light, there is a little want of “crispness in the definition,” as, with a strong light, the darkness of the shidow itself must of necessity be less than with a weaker light, because with the strong light the szadow must be more illuminated by light reflected from surrounding objects, although it may appear darker by contrast with the surrounding portion of the screen directly opposed to the light. : It seems not strictly correct to say that the removal of a light from an object makes the shadow less dense, as the shadow does not alter, although an appearance of less density is produced by the surrounding illumination being diminished. Again, when two lights are compared by contrasting the shadows which they cast, the shadows are each illuminated by the other light. Thus, supposing that at first the strong and the weak light are at the same distance from the screen, the shadow cast by the weak light being more highly illuminated by the strong light looks paler than the shadow cast by the strong one, but will be darkened by the removal of the Strong light to a greater distance, until both shadows become equally dark. The same result equalizing the shadows can be obtained by moving the weaker light towards the screen until the shadow from the strong light becomes as pale as that from the weak light.— Yours truly, G. H. SLIGHT. Lindisfarne, Romford-road, E. LANTERN ASSOCIATION. (Vo the Editor.) S1rR,—As a devotee of the lantern I came across your fifth number the other day, and now being aware of your existence, I hope that you can send me your first four numbers, and, in the next place, that you will allow me to havea little say on one or two matters 47 regarding those delightful studies in photography which the lantern enables us to prosecute with pleasure to ourselves and profit to many more deserving folks. The simple and delightful »zod¢us operand? of producing slides I believe is destined to become one of the most important branches of the great art ; and I agree with your correspondent how much more satisfy~ ing to the amateur of limited time is the making of slides to the production of silver prints. I see there is frequent allusion in your journal to the use of the lantern in connection with Camera Clubs and Photographic Societies. Three years ago this winter I ventured to suggest in the Photographic News the desirability of forming a Lantern Club pure and simple. So far as I know the suggestion did not take much root, and I now write to suggest the necessity, now that the lantern is so generally used and acknowledged as a power, that those who possess lanterns, are fond of working them, and wish to perfect themselves as manipulators, as lecturers, and as slideproducers, should club themselves together and form a Lantern Association. And I think they might have fortnightly or monthly exhibitions with great advantage to themselves and others ; besides, as is evidenced at the Photographic Exhibition, where the lantern evening draws the largest audience, we might be sure of ourselves getting good companies and good shows of pictures. I shall be glad if you, or some other persons of influence in the craft, would call together those interested, so that they might float the said club, for I am certain it would “go.’’—I am, yours very truly, 7, Maddox St., W. T. H. HOLDING. FADING OF SLIDES, (fo the Editor. } S1r,—I have to congratulate you on your very successful paper, which was much wanted, and seems to satisfactorily fill the requirements of lantern amateurs, &c. Will you kindly tell me, in your answers to correspondents, whether there is any remedy for photographic slides that are'turning white? Can varnish be used to fix them before they turn quite opaque, or have they become worthless? I have a lot of views photographed in Australia, and they are all going ““milky.”—Yours, &c., L. MOONEN. 8, Fellows-road, N.W: , [The slides have doubtless been intensified with mercury followed by ammonia; at any rate we are aware of slides thus treated that have assumed this appearance. For these, varnish does not prove a protection. We would suggest again placing them in a solution of bichloride of mercury until quite bleached, and then after a thorough washing, transferring them to a bath of sulphide of ammonium very greatly diluted. If this will not restore them, we know of no other means. Probably some correspondent may know of some better method ; if so we shall be glad to have his experience.—ED.] ee WHEN using eikonogen for developing transparencies, one drop ofa ten per cent. solution of bromide to each ounce of developer, will greatly improve the colour and clearness of the picture.—A. Cowan,