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4 The Optical Magic Lantern Journal and Photographic Enlarger.
as if then the light be insufficient it can be increased by adding another battery. As to the size of the batteries, the efliciency varies a great deal, and while the small size of some makers are quite powerful enough, the medium size will be found the best all round, although causing the case to be more bulky. It should be remembered that the flexible wire will take up a little current, and the whole battery should be sufficiently powerful when all is connected up to bring the filament of the lamp to incandescence just short of sparkling.
Now as to the purchases. batteries, a small incandescent lamp, a “ pear”
shaped push, and about six yards of flexible |
twin wire. ‘he case can be made of fretwood, if neatly dovetailed together, or stouter material if desired. The size of this case will, of course, depend upon the number of batteries used, and the measurements must be obtained by placing the cells together as compactly as possible, adding another two inches or so to the length for the lamp compartment. This lamp compartment should be lined with white card, so as to make the most of the light. The red glass cover is best fitted at the narrower side of the case instead of the top.
The electrical arrangement is practically the same as that of an electric bell set, the lamp taking the place of the bell. The batteries must be connected together in series, i.e., the inner or carbon terminal of one cell to the outer or zine terminal of the next, leaving a carbon terminal free at the one end and zinc at the other. The following diagram shows all the electrical connections :—
The following are a few concluding hints :— Before fitting the cells into the case, wrap them round with brown paper to prevent the metal parts touching where not required. If a knot is made in the flexible cord on the inside where it leaves the case, there is no fear of the joinings being pulled apart. The arrangement must not be used as a reading lamp, or kept alight for more than a few seconds at a time.
There will be the |
On the Development of Lantern Sildes.
By Duncan Moore.
Continued from page 218.
Once ascertained, there will be no difficulty in giving a suitable exposure to negatives of the
| same class, and with practice the examination of
the negative will at once indicate the exposure required. It should be seen that the negative and transparency plate are both flat and no irregularities on the surface. A very small knot in the glass under the film will very likely fracture the negative when pressed in the frame. By carefully looking over the surfaces of both negative and positive plate, any unevenness will be detected. A defective negative may be printed for a long time in the ordinary way Without coming to grief, but when pressed hard
: against another unyielding surface a fracture
soon occurs. Small splinters of wood from the frame, or other hard trifles, getting between the two glasses, generally results in disaster. The glass being curved, or of. unequal thickness, considerable pressure has to be applied to force the films into close contact; a trifle between them, that might not cause damage with less pressure, with the increased strain would almost certainly do so. ;
A small screen held in the hand, a piece of cardboard, or something of the kind, is useful to shade parts of the negative during exposure, whilst the light continues to act on some denser portions. Much better results may often be had by this partial shading from many negaThe screen must be kept gently moving during the time, and at not more than a few inches in front of the negative. A very thin negative is best copied by using a much weaker light than usual for negatives of ordinary density.
One very important precaution in copying by contact is the masking of the edges of the glass, either by an opaque paper mask, covering about a quarter of an inch of the negative all round, or by painting the edges and a quarter of an inch of the surface with black varnish. More transparencies are spoilt by neglecting this precaution than by almost any other. The light striking on the edges of the plate will fog nearly a third of the surface, and the brighter and nearer the light the more pronounced the. effect. With films, of course, there is little danger of fogging from this cause, or
; breakage by pressure.