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.
Catch-Lights In The Eyes. The catch-lights in the eyes being an exact reproduction of the source of light, are really the key to the lighting. If they are in proper position, the lighting will have been correctly made. A catch-light should appear in the upper corner of the iris of each eye; not directly above the pupil, nor at the side, but half way between these two points. This will indicate that the light falls upon the subject at the proper angle and, as the catch-light should not appear outside of the iris, the position of the head will be correct when the catch-light is in its proper location. If the catch-light is in the pupil of the eye it is evident that the face is turned toward the light at too great an angle. If it is in the white of the eye, it shows that the face is turned too far from the light. As a rule, in this latter position the catch-light in the shadow eye will be lost.
Relative Position Of Face And Body. The face and figure of the sitter give better lines when not placed in exactly the same direction. In making portraits of fleshy people, turn the body toward the light. This tends to lengthen the neck and apparently elevates the head from the shoulders. The neck of a slender person may be given a shorter appearance by turning the body from the light.
Pose Of Figure. For bust portraits of women or children the subject will appear better leaning forward in the chair, rather than backward. If, in a reclining position, the lines of the figure are not good, the waist line being bunched, with a more erect position, and the chest slightly extended, a more natural waist line may be obtained. A reclining position is more suitable for portraits of men, especially if they are of slender build. Leaning backward slightly gives the effect of stoutness; therefore men of excessive stoutness should sit more erect. If the lines are exaggerated they may be materially improved if careful attention is given to the trimming of the finished print.
Reflected Light. The less reflected light employed the better. In fact, one should always aim to make the best use of the direct source of light, taking the light from but one direction. Reflected light is a secondary source. The further the sitter is from the window, and the greater the diffusion of the direct source of light, the softer will be the shadows, requiring a decreased amount of reflected light. When it is necessary to further illuminate the shadows by means of reflected light, proceed cautiously, remembering that illumination of this kind should be simply a continuation of the direct source of light. Reflected light should not lap over the direct source of light, nor should it be thrown so strongly into the shadows as to cause the shadow side of the face to become as strongly lighted as the high-light side. Those portions of the face nearest the camera should be in strongest light, and from them there should be a gradual blending as the contour of the face recedes. The ear on the light side of the face will, of course, be in much stronger light than that on the shadow side, yet the light on the former should be much more subdued than the illumination on the front of the face. Flatness and distortion would result if the reverse of this action were carried out.