The Optical Magic Lantern Journal (November 1890)

The Optical Magic Lantern Journal and Photographis Enlarper. 49 tight receptacle for the plates, they are a convenient means of carrying a stock of plates. Fic. 1. To charge the camera, a magazine (Fig. 2) is inserted into the end of the camera by a sliding lid. This. is fitted with | rack-work, engages witha pinion, | the movement of which causes | chamber, which the plate box magazine to be raised or lowered so as to present any desired plate at an opening in the division placed in the camera as shown in Fig. 3. A series of numbers are marked on the side of the magazine; and when a fine line placed beside the number which is shown at a small Fic. 3, opening coincides with a similar mark at the edge of the opening it indicates that a plate is in exact register for being conveyed to the exposing frame. This frame is swung ina horizontal position by a movement of the large handle shown in Fig. 1, and just before it is quite horizontal, it engages with a spring flange, which acts as a light tight door to the slot in the division mentioned, and causes it to open. The horizontal carrier thus forms a continuation of the groove in the magazine presented at this opening. A slight tilt of the camera suffices to make the plate slide into the carrier, which is then brought to the perpendicular for exposure. As soon as the carrier is released from the horizontal position, the spring slide at once closes the slot, thus preventing the possibility of any light reaching the stock of plates during exposure. The lens is a rectilinear of sin. focus, and the shutter is one invented by this firm, and is of the plunge principle, occupies little room, and may be used either for time or instantaneous exposures. ; The most useful points in connection with this camera are, that the exposed plates may be removed and a fresh supply inserted in open daylight, as provision is made for closing the end of the magazine before it is removed from the camera; also that any particular plate may be exposed and returned to its place. Although the camera we tried was not provided with means for recording those plates which were exposed, _ we think that it might be advantageous to havea small ' slab on the upper part of each magazine, so that one ‘could if desired mark the nature of the plates with | which it was charged, and also a similar numbered slab on the camera itself, on which could be marked in pencil a tick against the numbers of the plates as they are exposed. This, however, would only be necessary when the exposures were not made according to the consecutive order of the plates. The camera being well made works with certainty. he Influence of Size in Lantern Objectives. vr Opinions of Experts—Messrs. Baker, Freshwater, and Traill Taylor. AT a recent meeting of the London and Provincial Photographic Association, the question of large or ; small objectives for lanterns was opened by Mr. T. F. ' Freshwater, who remarked that if you are using a ‘short-focus condenser, one that is usually supplied ‘with a lantern for limelight, you will find the cone of ‘light comes down to such a point, that is, about gin. before it crosses. Now if you place a Gin. lens in this cone at its right place—that is, at its focus with the picture in the lantern —you will see that the diameter of the spot of light is about rdin. in diameter. So you see a 2in. lens is quite large enough to pick up all the rays from a qin. condenser and carry them to the front combination ; but if you place an 8in. lens, this same cone of light has come down very much, and is almost on the cross, so that there is not enough light to fill the lens so as to illuminate the whole of the disc, as I shall presently show. I intend to put on lenses of different forms—the old meniscus pair, single achromatic, using in front of both of these a stop about one-third of the diameter of the lens. This stop is necessary to cut oft the outer pencils of light and give a flatter field and better definition. The other lens is a combination of the portrait form, but altered in the curves to give a flatter image on the screen. Now if you use a large lens of this form of about 8in. in focus with the same condenser, you will undoubtedly gain some considerable advantage; it will pick up the rays better than the small lens and cover the disc much better, but you so increase the size of all your fittings and the weight of your lantern you have to carry. Some will say that is of no consequence ; you must have acab; a pound or two is of little moment. That is all very well, but a set of such lenses is rather a serious matter. Now if you alter the condenser in such a way that the cone of light is longer, you will then illuminate the smaller lens, as I will show, and get as good a picture as with the large objective. Then comes the question of definition. It does not matter for long-focus lenses what form is used ; a single lens will give just as flat a field as a compound lens, and pass more light. This will apply to lenses of above roin. in focus. After some minor discussionZrelative to’the size of ee eee Oe