This section is from the book "Modern Photography In Theory And Practice", by By Henry G. Abbott. Also available from Amazon: Modern photography in theory and practice: A hand book for the amateur.
12 ins., size of paper; 3 ins., size of image; 25 feet, distance from wall; 4, the proportion.
12 ÷ 3 = 4; 25 X 4 = 100; 4 + 1 = 5; 5 X 5 = 25. 100 ÷ 25 = 4, the focal length of lens.
Enlarged bromide prints can be made by the amateur by means of any ordinary camera which focuses from the front and the necessary adjuncts are very inexpensive. These enlargements can be made in the daytime or during the evening, the source of light being the only difference. If they are made in the daytime, a room having but one window and that one facing the north, should be selected. Procure a few sheets of heavy red express paper, the kind used for doing up large packages. Measure the size of the window, including two inches on each side and the top and bottom. Glue two or three sheets of this paper together until you have a sheet which is large enough and then trim it to the required size. Put this sheet up in the window casing and hold it in position by means of thumb tacks. Draw a kitchen table close up to the window and place upon it a box which will hold your camera. Now place your camera on the box, the lens pointing into the room. With a lead pencil, mark an oblong on the paper the exact size of your negative, cut a piece from the paper this size, so that when the camera is backed up to the window all the light will come in through the camera and lens. Now glue some wooden strips around this opening, on each side and the bottom and push three thumb tacks into the wood, so that the negative can be dropped in from the top and will be held in position by the thumb tacks, as shown in Fig. 50. All the preliminary arrangements can of course be made by gaslight. A drawing board, a baking board or any other smooth piece of lumber, should now be selected for holding the bromide paper. This can be held in a vertical position by means of triangles or brackets screwed to the back, as shown in Fig. 51, or by making a groove in a piece of 2 x 4 lumber and inserting the board in the groove, as shown in Fig. 52. The board may also be held in position by tying it with a piece of string to a soap box. To this board fasten a large sheet of white paper and place the negative in the groove in the window. The ground glass is now removed from the back of the camera and that instrument drawn close up to the opening. Select the
Fig. 51 largest stop or diaphragm and open the shutter and you will find an image on the white paper when you turn out the gas. Push the drawing board to and fro until you get the enlargement of the proper size and in the center of the sheet. Now by racking the camera bellows in and out, proceed to sharpen up the image just as you would focus on the ground glass. If the negative was turned upside down and with the film towards the light, you will have an image just as the scene appeared in nature. You can now continue further operations by means of the dark room lantern. If any light leaks in around the camera where it joins the window, shut it out by means of the focusing cloth, for there must be no white light in the room aside from that which comes in through the negative and lens. With a lead pencil indicate the image on the white paper so you will know just where to locate the bromide sheet. You now close the shutter or cap the lens and opening the envelope containing the bromide paper, you proceed to place a sheet in the proper position by means of the marks made and hold it flat, avoiding all wrinkles, by means of four thumb tacks. You are now ready to make the exposure but before doing it, it would be wise to first try a small piece of the paper in order that you may make sure of the time. There is no rule that can be laid down as to time, any more than we could do in making a negative. The sensi-
Fig. 52 tiveness of the paper, the density of the negative and the brightness of the light are all factors on which the exposure depends. We can only determine the proper exposure by experiment but it is not necessary to spoil full sheets in order to determine the correct exposure. The best way to do this is to cut a narrow strip from one of the sheets and pinning it in position proceed to expose it as follows: Pin a sheet of paper, white or colored, over the bromide strip so as to cover three-quarters of it and then opening the shutter give it a half minute exposure; close the shutter and pin the sheet so it covers one-half of the bromide slip and again expose for half a minute and so on until the last quarter of the sheet is exposed. It will be evident that we now have a strip of bromide paper with four separate exposures on it, one of a half minute, one of a minute, one of a minute and a half and one of two minutes. By developing this strip we can readily determine which is the best exposure for our negative and govern ourselves accordingly. The larger we make the bromide picture, the longer will be the exposure required. Now, before making the exposure on the large sheet, proceed to stop down to say f 16, as this will sharpen up the image considerably but will increase the length of time of exposure, the stops working just as they do in making a negative. What we said in regard to the camera facing the sky when making lantern slides, holds equally good in making bromide enlargements. If your window will not admit of an uninterrupted view of the sky, then you will have to place a sheet of white cardboard just outside your window, on an angle of 45°, so as to reflect the light from the sky through the negative. Fig. 53 will give you a general idea of the arrangement of the camera, table and bromide paper when making enlargements by daylight. You will observe that it is necessary to elevate the camera above the general level of the table if we expect to make any material enlargement, so that the lens will come opposite the center of the bromide sheet.