HARDENING THE FILM.
To further preserve the slide it should be varnished ; but we do not care for the usual transparency varnishes, which are slow dryers and frequently accumulate dust on the surface and spoil the slide in the lantern. The best varnish is a celluloid one, such as Hartley's, and this sinks into the surface of the film, dries hard, and is waterproof. To varnish the plate, it should be held on the tips of the fingers of the left hand, or better still, supported by an India-rubber pneumatic plate-holder. A pool of varnish is then poured on to the plate and the holder is gently tilted, so that the varnish successively runs to each corner, finishing with the right-hand corner nearest the operator, who then allows the surplus to flow off into the bottle which is held to receive it. When varnishing do not try and put on only just enough varnish ; pour on plenty, for if the plate is held steadily it will not run over the edges, and the surplus can always be poured from the corner of the plate into the bottle. The plate being varnished, set it in such a rack as the Sinclair Ideal Rack, so that any surplus varnish drips from one corner on to a sheet of paper placed under the rack. After the plate has drained for about 5 minutes there is generally a drop of varnish on the lower corner of the plate, and this may be gently removed with a clean cloth, touching the extreme edge.
The Sinclair Draining Rack.
While lantern slides can always be made by contact from portions of negatives, still the pictorial worker who has composed his picture on the plate, wants the whole of it reproduced on the slide, and for doing this we must use a reducing camera. In our own practice the majority of our negatives are quarter-plates, taken with a hand camera, but as we always try and get the best composition in these small plates, it is very rare for us to use the contact method. To reduce, we have to re-photograph the negative on to a lantern plate, and this necessitates our placing the negative in such a position that light can pass through it. This may be done by fixing the negative in the window of a room and copying it by means of a stand camera with sufficient extension, but obviously such a course is a slow and trying one, because the negative, lens and plate should be parallel with one another and in the same optical axis. We use a lantern slide camera, as shown in the illustration. This consists of a baseboard on which the camera, which has a bellows extension of 18 inches, can be easily moved backwards and forwards, and the back of the camera has a rack and pinion for fine focussing. There is also a swing back, to correct any lines which may be out of the vertical in the negative from which the slide is being made. The front of the camera takes our lens, which may conveniently be of 5 or 6 inch focus, and this lens projects into the fixed box at one end of the base. This box is fitted with an adjustable carrier, which will take 1/2-plates or any smaller size, by means of inner frames, and the carrier, being movable vertically, horizontally or diagonally, permits of the horizon line being placed parallel with the edge of the lantern slide, even when it is out of position in the negative. The dark slide is a single one. When using such a reducing camera we must point it towards the sky, taking care that an imaginary line drawn from the lens through the negative would, if continued, not be interfered with by houses or trees. This is not always easy in town houses, unless we have a room near the top of the building at our disposal, and, should we not have such a position at our command, the camera may be kept horizontal and pointing towards a window in which there is a piece of ground glass, somewhat larger than the negative, and about 3 inches from it. The ground glass should be of the fine or focussing screen variety, and may with advantage be slightly oiled so that, more light passing through it, the exposure may be reduced.
LANTERN SLIDES BY REDUCTION.
The Sinclair Lantern Slide Camera.
The time to expose may seem a difficult problem, but after a few trials, drawing the shutter of the dark slide as suggested when making contact slides, we shall find the proper time. Of course, the fact that daylight is constantly varying may cause trouble, and our method when we used daylight was to always test the light with a Watkins Meter held in the position occupied by the negative, or rather just by its side, for we used to expose the meter and camera simultaneously. Supposing we found that an exposure of two minutes was required on a day that the meter took 30 seconds to darken, we are fairly safe to assume that when the meter took 15 seconds our exposure should be one minute, and if the meter required one minute then our exposure should be four minutes. The times mentioned are, of course, only suggestive of the principle, and are not the identical times, which we have now forgotten, and would, in any case, not do for the negatives of others. We may say that we prefer the Watkins to the Wynne Meter for this purpose, because the Watkins paper taking about twice the time to darken, there is less likelihood of error. For many workers, business engagements, prevent other than night work, and in these cases the reducing camera must be used in connection with artificial light. The best plan then is to place the reducing camera on a table and to have a condenser, such as is used in enlarging lanterns, and of sufficient size, arranged on a block so that it is parallel with the surface of the negative, and a sheet of finely ground glass is placed between the condenser and the illuminant. The stronger the light the better, and electricity in the form of a Nernst lamp, or small arc lamp, is desirable, but failing this an oxy-hydrogen lantern jet does admirably, after which we should suggest acetylene. The objection to weak light, such as that given by oil lamps, is the long exposure required. To give some idea of the exposures necessary when working in this way, we may say that when reducing from 1/4-plate to lantern size, using a No. 3 Kama lamp, 220 volts, f/8 stop and 6-inch condenser with ground glass interposed between the light and condenser, and using a Paget Slow Lantern Plate, we give exposures of from 15 seconds to two minutes, according to the density of the negative. When using artificial light for reducing it is necessary to get it properly centred so that there is equal illumination all over the negative, and the order in which our outfit is arranged is as follows : -