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.
62. The angle of light is obtained by manipulating the opaque shades directly over the subject, while relief, roundness and atmosphere are controlled by the opaque shades farthest from the subject. With the skylight entirely open, and too much top-light falling over the head of the subject, there will be a hard outline of the high-lights, and shadows altogether too strong. If the entire volume of light falls upon the front, the features will be flattened and any defects of the subject will be accentuated to the extreme. Light coming from behind the sitter and on or below the level of the head, with no top-light, gives large and strong shadows on the side of the subject. If this same side-light should come from the front, the amount of shadow is reduced; yet it is impossible to properly illuminate all the features and secure proper modeling unless the correct proportions of top, side and front light are employed. Only in extreme cases need any consideration be given to back light.
63. Most photographers exhibit a tendency to use a narrow, or extremely small volume of light, even when they possess a large skylight. They cut off the light with curtains, using but a small portion of it. With a narrow and more concentrated light one may see the effect of lighting more readily, but the time of exposure is, of necessity, so long that the subject loses expression. In order to retain expression the operator is often tempted to shorten the exposure, which results in under-timed plates and con-trasty negatives. It is not necessary to narrow the light to obtain the effect desired. It can be done more easily with an open light, in which case the exposure is reduced to a second or two.
64. You should be able to place the subject within the range of your skylight, and secure the correct angle of light by arrangement of the shades. However, it requires careful judgment and a thorough knowledge of the effect of light to properly place the subject, and then arrange the shades to reproduce the characteristics of the individual most truthfully.
65. It is most essential that the face be illuminated to a greater extent than any other portion of the subject, and it is only by having light concentrated on the face that this effect can be secured. Always place the sitter in the strongest light. It is seldom advisable to use a skylight wide open - i.e., without employing shades-because in order to light the subject properly, a square-shaped light seldom answers the purpose. If the size of the room is limited, it may be impossible to place the subject far enough away from the skylight to leave the light completely open, yet always have it follow out the correct angle on the subject. For that reason, it will be necessary to reduce the opening with the opaque curtains, or, rather, cut off a portion of the upper part of the skylight.
66. It is necessary to have the opening in the skylight conform to the space in which you are able to work. With a large skylight and a narrow room, you would not be able to get far enough away from the light to secure the correct angle and still use it wide open. The strongest light would be directed over, instead of falling on, the subject. Therefore, it will be necessary to curtain and cut off the excess top-light so as to secure the proper angle, and have the strongest light fall where it belongs. It may be taken as a general rule, that the shade directly over the subject should be drawn down sufficiently to obtain the angle of light; the next shade should not be drawn so far, and the third less than the second. The first section controls the angle of light, the second is drawn merely far enough to assist in carrying out the angle, while the third and fourth assist the second shade.
67. In this manner a general distribution of the light throughout the room is obtained, permitting it to surround the subject. The exact shape and size of the opening depend entirely upon the requirements. As the shades directly over the subject regulate, to the greatest degree, the angle of light falling on the subject, they should receive first consideration, being drawn so as to give the proper angle. The roundness, or amount of relief, depends largely on the remaining shades, while the position they should have is governed entirely by the nature of the subject. For instance, if your subject possesses a thin face, it will be necessary to illuminate the hollow cheeks and give an effect as round and full as possible. Therefore, the portion of the skylight in front of the subject should be opened to a greater extent than if the subject had a full, round face, which would not require as much illumination to fill out and round the shadow side.
68. It makes no difference whether working with a single-slant, double-slant (hip-light), or perpendicular light,-the general principles remain exactly the same. The manner of controlling the light, however, varies not only with the shape but with the size and location of the light. A wide skylight will naturally admit a more general and even illumination throughout the room. It reduces the density of the shadows, which is one of the most essential features to take into consideration in securing atmosphere, or roundness-which give the effect of relief. The location of the skylight has much to do with the ease of controlling the light. It is preferable, by far, to have a north light, because if the skylight faces the east, west or south, there will be times when direct sunlight will strike the glass; and as the amount of direct sunlight is continually varying, it will give no end of trouble. The strength of the light should be just as great from one section of the skylight as from another, but this is seldom the case.
69. If a studio, with skylight facing the north, is situated on the top floor, with no other buildings near, ideal conditions would exist, as the whole force of the light reflected from the heavens will evenly illuminate the skylight.
However, when the studio is on the ground, first or second floor, with buildings opposite, which either obstruct or reflect light, it is quite impossible to secure an even illumination. In such a location it will be found necessary, by arrangement of the curtains, to cut off strong reflections and balance the light so as to concentrate the strongest part on the subject. You should be so familiar with the skylight as to know approximately the place in which to locate your subject, at any hour of the day, in order to secure desired effects.