This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Copying With A Box. Another very simple method is as follows: Procure an ordinary box, about 8 inches square and 14 inches long. Close one end of this box, and cut an opening in it the size of the plates to be copied. A box of this size is suitable for copying 4x5 and 5x7 negatives. On the outside of this opening fit a grooved strip, top and bottom; in this groove slide your negative to be copied. Paint the inside of the box a dead black, to prevent reflections.
898. To copy a negative place the box on a table, close to a window, and on a level with it. Extend the bellows of the camera and place one end inside of the box, telescoping it. The box will exclude all light from the lens, except what comes through the negative, and good slides can be made in this way. It will be necessary, in order to evenly illuminate the entire negative, to place the ground-glass frame in front of the negative-within one inch of it-just the same as if the copying-board were employed.
899. Taking it for granted that the image has been reduced to the correct size, and the proper focus procured, all is now ready for exposure. To do this, use a cap on the lens or the regular shutter. When using the cap run your hand underneath the cloth and take off the cap. In doing so, be careful not to shake the apparatus. If properly made and set up, a slight shake would have no effect on the slide, as both the negative and slide would receive the same movement. Whenever it is possible make exposures with the shutter on the lens, thus avoiding any possible jarring of the camera.
Length Of Exposure. So many factors have to be taken into consideration, that it is not possible to state definitely the proper length of exposure, but one or two plates devoted to testing this will soon teach one to judge properly the exposure necessary. This same method can be applied when using artificial light. In Illustration No. 13 is shown a convenient box for electric or lamp-light, which must be placed in position behind the negative and ground-glass, the light, as already explained, being placed far enough away from the ground-glass to illuminate evenly the entire ground-glass and negative.
901. The length of exposure by artificial or daylight depends largely upon the strength of the light and density of the negative. The best plan is to sort all the negatives from which slides are to be made, into grades of density. Take one of the most dense and make an exposure from it as a guide. Expose one-fourth of the lantern-plate for five seconds; draw the slide to one-half of the plate and give five seconds more; draw it to three-fourths and give five seconds more; then withdraw the slide completely and give five seconds exposure on the entire plate. The first fourth of the plate will have had 20 seconds, the succeeding fourths 15, 10 and 5 seconds respectively. After development, the time on one portion of this plate should be correct. Use this as a guide. If the negative is very dense give double the time on the test plate. It should then be easy to figure the time on the thinner negatives; for if they are only half as dense only half the exposure will be needed.