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.
36. Lighting is the art of reproducing the characteristics of the subject by the correct application of light and shade. It is necessary to have light to produce an effect on the sensitive plate, but why is it necessary to control light? Why is it necessary to have the light fall on the subject at a certain angle, and why must the light be of certain quality ?
37. Not only must consideration be paid to light, but due attention must be given to shadow also. Light without shade will not produce a pleasing portrait. In fact, the beauty lies in the delicate half-tones and shadows to fully as great an extent as in the high-lights. It is the control of light, no matter whether the picture is made in open sunlight or in a studio, that gives the proper relationship between light and shade.
38. To obtain the most artistic result the light must come from one source only and fall on the subject at the right angle. This angle is determined by the effect produced on the subject. If all top-light is employed, deep shadows will be cast by the eyebrows, nose, lips, and chin, making the eyes appear deep sunken and the other features distorted. On the other hand, if the illumination is all from the side, heavy shadows will be cast across the shadow side of the face, the light side being extremely white and chalky. If a mean between these two extremes is chosen and the light allowed to fall on the subject at an angle of 45 degrees, the light will illuminate all lines on the face as well as both eyes, and accentuate the strongest characteristics which show in the face of the individual.
39. Having obtained the proper angle of light, it is next necessary to control the harshness; for, if allowed to strike the subject with full force, the light side of the face will be too chalky, while the opposite side will be too much in shadow, giving practically no detail in either the highlight or the shadow. By diffusing or reducing the strength of the light the rays will be distributed and, although not as powerful, will spread over a larger area. If a piece of cheesecloth or semi-transparent material be placed over the window or skylight, the high-lights on the subject will be considerably reduced and, owing to the general diffusion of the light throughout the room, the shadows will be illuminated to a certain extent, so that there will be flesh tones throughout the entire face.
40. Where the source of light is small, the light will be extremely contrasty and it might not be possible to spread it sufficiently with the diffusing curtains. In this case, the shadows not being illuminated sufficiently, it will be necessary to resort to the use of reflected light. For this purpose a white reflecting screen should be placed opposite the source of light and turned at such an angle as to throw the strongest reflected light on the front of the shadow cheek. To accomplish this, the screen is usually placed at an angle of about 45 degrees to the side-light.
41. One principle always to bear in mind when making portrait studies, as well as when photographing any subject is: The strongest reflected light should fall on that part of the subject receiving the strongest direct light. From this point there should be a gradual blending back into shadow as the distance from the camera is increased. When a subject is posed to secure a front view of the face, the nose and the front of the forehead, the cheeks, lips, and chin should be in highest light. The back of the cheeks, the ears, and the shoulder farthest from the camera may be in shadow, the degree depending entirely on the nature of the subject and the effect it is desired to produce. For profile and shadow lightings, the reflector should be so placed as to reflect the strongest light into those portions receiving the strongest direct light, thus rounding them off and gradually blending into the shadows.