Hitherto, in dealing with the production of lantern slides, we have supposed that the negative employed is of such a size that it can be reproduced as a positive by contact printing in the ordinary printing frame,
Occasionally, however, the operator will have a negative of larger size which he will be anxious to reduce to the standard lantern size. Let us suppose*, for instance, that he has a whole-plate negative ( 8½ X 6½ inches) and that he requires to reduce this to lantern size (3¼ inches square). It is quite plain that the contact method will not do here, unless he requires but a quarter of the negative to be reproduced. The reduction must be made by means of the camera, with such additions as any amateur worker can arrange for himself in a very short time.
Upon a deal table nail a couple of laths at such a distance apart that the camera will slide to and fro between them, like a tramcar on its rails. At one end of this miniature railway, place a small lidless box - a packing case will do - with its open end facing the camera. In the bottom of this box a hole should be cut (8½ X 6½ inches) to fit the negative. A groove top and bottom, made by nailing slips of wood on the outside of the opening, will hold the negative in position. Outside the box place a sheet of stout card at an angle of 45 degrees, so that the light from the sky is reflected through the negative. (We are to suppose that the work is being carried on out of doors, or at any rate in some kind of glass-house.) Between the open box and the camera, and on the upper part of each lay a couple of light wooden rods, and over these put a dark cloth. We must now see to the camera. If it be larger than quarter size, the ground glass screen should have pencilled upon it a 3¼ inch square, as a guide to the size of the picture required. The dark slide too must be furnished with a carrier to hold a 3¼ inch plate. The lens employed should be of short focus, the wide angled doublet, or portable symetrical, shown at Fig. 21, being suitable for the purpose. A rapid rectilinear, or a portrait lens can be used, but neither of these will give quite such good result: as the one just recommended.
The picture must be carefully focussed, using the largest stop in the rotating diaphragm. In this, great advantage will be found in using a focussing glass, which can be purchased for a few shillings. The glass is held touching the ground glass screen of the camera, and the eye is applied to the smaller end of the brass tube in which it is mounted. A good focus can be more quickly obtained by means of this glass than with the unaided eye. By moving the camera to and fro between the laths nailed to the table, and by working the focussing screw of the camera, it will be found easy to get the image on the screen down to the correct size.
With regard to the exposure necessary to ensure the best results, we must once more speak rather vaguely. It depends upon the light, the density and colour or the negative, and the lens employed. But supposing that the light be good, and to consist of the reflected light from a clear blue sky, that we employ the smallest stop but one of the portable symmetrical lens, and that we are using a first-rate whole-plate negative, with a fairly rapid plate in our dark slide, the exposure will be about two minutes.
Lantern slides after being dried do not require much further treatment. If used uncoloured they ought to be varnished in the same way that a negative is varnished. Coloured pictures are protected by the medium used as a vehicle by the painter, which consists of thin varnish. In any case they will require to be mounted with a thin cover glass, and between the two glasses is placed a paper mask. These masks are made of black paper and can be bought ready cut with a round, square, or cushioned-shaped opening. A landscape will generally look best in a round mask, but occasionally when a figure is standing at one side of the picture part of it might be cut off by that shaped opening, in which case a cushioned-shaped mask must be employed. For architectural subjects the square mask is most suitable;
The two glasses with their intervening mask must now be bound together by a slip of gummed paper. The black paper known as needle paper is the best to employ, and the gum which sticks most firmly to glass, is made as follows: -
Dextrine ... ... ,.. 1 ounce.
Loaf Sugar ... ... ½ ounce.
Mix into a mucilage with warm water, and leave on the hob for an hour or two until thoroughly transparent. One side of the needle paper should be gummed with this mixture, and when dry the paper can be cut into strips 3/8ths of an inch wide and 14 inches long.
To bind a slide with one of these gummed slips, damp the gummed side of the paper with a sponge or with the tongue, and place it before you on the table. Now take a lantern slide and place one edge of it at the end of the strip, and exactly in its centre. Now turn it over and over on the strip until all four edges are covered, and in the meantime press down the edges of the paper so that they will lap over, and fasten the two pieces of glass rigidly together.
Some kind of slide holder is required before the pictures can be shown in the lantern. Professional exhibitors use a separate mah ogany frame for each picture and the picture remains in it. But for amateurs this plan is needlessly expensive. A good plan is to employ what is called a panoramic slide holder, which consists of a frame having a groove at the top and bottom, through which the pictures can be passed in turn, one picture pushing out the other which has been already shown.
There is also another slide holder which can be well recommended. This consists of a frame to fit the lantern, within which slides a double holder, with places for two pictures. While one picture is being shown the other is outside the lantern, and can be changed for the one next in order.
A well executed photograph on glass, prepared for the lantern, is a photograph at its very best. A picture of the same size on paper would in comparison give a very poor effect, for the grain of the paper destroys in a measure the finer details. But in a picture on glass there is no grain, at least no visible grain, and when thrown on a screen by a good lantern, it can be viewed by a number of people at one and the same time. The amateur photographer will find no end of pleasing occupation in translating his negatives into this form. Still more pleasure will he find in describing his rambles to his friends, accompanying his remarks, by first-rate pictorial illustrations.