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.
The Eyes. Without regard to the position assumed by the subject, the eyes must lead the face under all circumstances. If the face is turned to the right the eyes should lead a little more to the right. If the face is directed to the left, then the eyes must lead to the left. Not only should the eyes lead the face, but they should also be inclined slightly upward - just a trifle above the level. This gives better expression, and more roundness is produced than if they were drooped, or even on a level. A drowsy, sleepy appearance will invariably be the result if the eyes are turned downward. An excellent rule to follow is never to permit the white of the eye to show below the iris. While the mouth controls the principal facial expression, the eye is a close second in importance. By properly directing the gaze of the eyes, not only is it possible to maintain a pleasing expression, but a too serious one may be modified to some extent.
Note. It must be understood that these suggestions and rules pertain only to Plain Portrait Lighting, and do not apply to extremely odd posings and lightings of Genre type. In producing work of the latter character be guided entirely by the effects desired.
Catch-Lights In The Eye. The surface of the eye, being a reflecting medium, acts like a mirror and reflects the light coming from the window. The location of this reflected spot is governed entirely by the angle of light as it falls upon the subject, and the turning of the face toward, or from, the light. This spot is termed a "catch-light," and its size depends upon the distance of the face from the light, also the size of the source of light. If the lighting has been correctly made, the catch-lights will appear in the upper corner of the light side of the iris of each eye. Upon close examination this catch-light will be found to be an exact reproduction of the window or other source of light.
The catch-light must not extend into the white of the eye, nor should it touch the pupil.
Eye Rest. The ideal eye rest is the face of the photographer. One who is clever can instantly change the expression of a subject if the eyes rest upon him. By raising or stooping the eye can also be guided for height. It is possible to cause the eye to lead the face at any desired angle, by simply moving about, more or less, in one direction or another. Another advantage of the human eye rest is that, at the proper time, a word from the photographer will bring an expression that otherwise might be impossible to obtain. Of course, practice and experience are required before one can properly take the part of a human eye rest.
248. Then, too, there are people who cannot look at any one during an exposure. In such cases the photographer may hold one hand in the direction it is desired to have the subject look, requesting that he rest his eyes upon it. Or, a photograph attached to a cord and a rod having a substantial base, will answer. Attach the picture in such a manner that it will slide up or down freely. It will be necessary to place this rod at just the right distance from the subject, as the focal length of the eyes of all subjects is not the same. Observation will demonstrate that by placing the eye rest at a stated distance the pupils of the eyes of various subjects will grow larger or smaller, and often the eyes will assume a staring appearance.
249. Watch closely, placing the eye rest at a distance where the subject will experience no difficulty in viewing the picture. Some subjects are inclined to wink a great deal during exposure. Ordinarily this will do no harm, unless the winking is excessively frequent, when it is liable to cause a slight blur over the eye which can only be remedied by etching or retouching. Natural winking of the eye always results in good expression, providing the subject does not turn the eyes from the direction of the eye rest.
250. Never direct the subject to look at any particular point until the slide in the plate-holder has been drawn and everything is in readiness for the exposure. Then, without further caution, and with no apparent exertion on your part, attract the attention of the subject by speaking, advising them to follow your eyes. While talking, at the moment the proper expression is secured make the exposure. Where a subject cannot follow your eyes an eye rest may be employed. Suggest that they look at it for a moment; then, when the expression becomes natural, instantly make the exposure. A pleasant remark from you at the same time of making the exposure will frequently add materially to the expression and likeness.