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.
Lighting The Subject. Refer to Illustration No. 24, and observe that the skylight is almost wide open, there being sufficient space beyond the end of the skylight to arrange the subject and background. The only shade used is the first one on the skylight, which has been partly drawn, preventing strong light from being carried too far across the face. For this variety of lighting the subject must be placed back from the light to permit all the illumination to fall on the sitter from the front. (See Illustration No. 26.)
Controlling The Light With The Diffusing Screen. The light is controlled entirely by the diffusing screen, which is placed between the light and subject, while the tone, or key of light, is obtained by placing the screen or to, or farther from, the sitter.
286. If the diffusing screen were not placed between the light and the sitter, heavy shadows and strong highlights would result. In fact, the effect would be quite contrasty. By softening the extreme high-lights with the diffusing screen, the same service is also performed for the shadows. Experiment by placing the screen at various distances from the subject, observing the different effects produced.
287. When using the diffusing screen think of it as your skylight. By separating, or closing, the small curtains at different places on the screen, and also by tipping the screen forward at the top, every ray of light can be controlled and directed to secure the desired result. For this style of lighting all the dark opaque curtains should be drawn on the diffusing screen except, perhaps, the top row. Where the opaque curtains cut off too much light from the drapery, separate them to allow the illumination to filter through the tan curtains on to the drapery, thus supplying catch-lights. The narrower the opening the more concentrated and snappy will be the catch-lights, while the increased separation of the black curtains produces broader light upon the drapery. By properly handling the screen sketchy effects may be obtained, with soft negatives full of detail and atmosphere.
288. It is essential that there should be detail in the drapery, as well as in the shadows of the face. Photographers sometimes carry this diffusion to the extreme, losing all semblance of detail in the drapery. This is wrong. There should be sufficient detail in the drapery to leave no doubt as to the texture of the goods. It is far better to light the drapery one tone too high than too low.
289. When photographing white drapery in this manner the diffusing screen is a great aid, because the light can be softened on the drapery and the face and flesh tints brought up to the same key, producing true values and avoiding dark faces. For dark drapery it will be necessary to separate the curtains on part of the screen, to illuminate and supply high-lights and build them up in proportion to the values of the face. This will also supply soft detail and avoid the mushy, muddy effects so frequently seen.