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.
Applying The Diffusing Screen. The diffusing screen also serves as a secondary light controller. With the opaque shades on the skylight the angle of the volume of light is controlled. With the diffusing screen the strength of the light upon the subject and also the catch-lights are governed. At the same time it controls the general balance of light and shade upon the face and drapery. Using this diffusing screen, placed between the light and subject, you can practically disregard the shades on the side-light, as all side-light may be controlled by this screen.
The Use Of The Diffusing Screen. By reference to diagram of floor plan showing this style of lighting, you will observe the location of the diffusing screen, placed been the light and the subject. When arranging the dif-fusing screen, remember that the object of the screen is to control the catch-lights and diffuse the volume of light as it falls upon the subject. In other words, it is a skylight within a skylight. The catch-lights, or high-lights, are supplied by direct light, through separation of the curtains on the upper row of the screen-sufficient to admit of as much white light as is required for the catch-lights. The remainder of the curtains are closed, the light filtering through the tan curtains, thus supplying diffusion. By placing the screen too close to the subject the light may be diffused to the extreme and produce flatness. On the other hand, to place the screen too far away would cause loss of control over the volume of light and give too broad a light. A mean between the two will give proper gradation, supplying roundness and sufficient brilliancy to give a clean, crisp negative.
124. By having the screen facing the front of the subject the light can be thrown more to the front, accentuating the high-lights in this portion. By turning the screen away from the front more light can be cut off from the rear, thus producing broader light on the front. For general work only the tan curtains on the screen will be required. The black curtains should be drawn to one side when not in use.
125. A most important point to be remembered is that the catch-lights (little high-lights) must be supplied with white light, and not by light filtered through the tan curtains, as this color will give a flat high-light. For this reason the tan curtains must be slightly separated on the screen, to permit white light to fall upon the sitter and supply light for the high-lights. For the half-tones and shadows the light is filtered through the curtains, thus giving snap, and softness as well. If the light used is extremely strong, supplying too hard a high-light, draw a section of the white diffusing curtain on the skylight just enough to soften the high-lights. Control the remaining light with the diffusing screen.
Illustration No. II Plain Portrait Lighting-Floor Plan.
See Paragraph No. 128.
127. The subject being properly placed with regard to the strongest light and its correct angle, turn the face toward the light until the tip of the shadow from the nose just touches the shadow of the cheek. (See Illustration No. 9.) If the shadows are too hard and dense and end abruptly next to the high-lights, and the high-lights themselves are hard, it will be necessary to use the diffusing curtains on the skylight, drawing only one section of curtains across the skylight until the high-lights on the subject are softened. When this is accomplished, you will usually find that the hard lines between the high-lights and shadows will have disappeared, and a sufficient amount of detail secured in the shadows. If, however, this does not give the desired amount of softness, it will be necessary to use the reflecting screen.