The greater appreciation and increasing use of flashpowder shows that the photographer is quick to realize the possibilities of the use of what we may call home-made sunlight. A flashlight is practically an instantaneous burst of bright sunshine. It has one great advantage over sunlight in that it can be produced in places where sunlight never penetrates. We can make our sunlight wherever and whenever we wish.

It is to be expected that the sudden production of a flash of light as brilliant as sunshine, in comparative darkness, must have a very considerable effect upon the eye - an organ which is as sensitive as it is wonderful. While the eye can accommodate itself readily to differences in illumination as much as a million to one, which is equivalent to bright sunlight out-of-doors and a dark night out-of-doors, the changes are usually made more or less gradually. When a change in illumination of anything like this range is made suddenly, some unusual effect must be produced upon the eye.

To find what these effects are, some very interesting experimental work has been carried out at the Research Laboratory of the Eastman Kodak Company. It is well known that the eye seeks to protect itself against sudden changes of brightness. One way is by the involuntary contraction of the pupil of the eye and a further protection is the closing of the eyelid by a wink. These are known as reflex actions and we have no control over them. A study of this reflex action of the eye must be of considerable interest to the portrait photographer who does any flashlight work.

It has been found by careful experiments that the reflex action of the eye can be photographed and actual measurements made of these movements. This is done by the aid of a motion-picture camera, which can be speeded up so that pictures can be made at the rate of thirty-two per second.

Focusing the eye in daylight the motion - picture camera is started and the flash set off fairly close to the subject. The results are shown in Figure 1. The pictures were made at the rate of thirty-two per second, the actual exposures, however, being only 1/64th of a second each as the shutter opening is closed for 1/64th

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Fig. 1 while a new portion of the film moves into place for the next exposure. In the first three pictures we see the eye in its normal state, the flash was then fired and its closeness to the subject is shown by the over-exposure of the fourth and fifth pictures which get the full benefit of the flash which lasted for the time of two exposures and two intervals and was therefore equal to one-sixteenth of a second. By this method there is, of course, a possibility of the introduction of a slight error, in case the flash commences while the shutter is closed, though this error may be reduced to a minimum by making the shutter blade opening as large as possible, thus reducing the pull-down interval.

As before stated a sudden change in illumination produces some unusual effects on the eyes and we have pictures of what actually happens in Figure 1. The reflex action, by means of which the eye seeks to protect itself, is shown in the sixth, seventh, eighth and ninth pictures, where we see the eyes gradually close and open in a wink. In the tenth picture they are practically normal again, though it will be one or two minutes before they are absolutely normal as in the first three pictures.

It will be noticed that the reflex action or wink did not begin until the third exposure after the flash had been fired, so that the subject faced the light for a little more than two exposures and the time intervals between, a total of about a twelfth of a second after the flash was fired. The wink lasted for one-eighth of a second, or a period of time during which the camera recorded four exposures. The time for this reflex action to occur varies slightly with different people, but in no case was it found to be less than one-twelfth of a second. There is just a possibility that the natural wink of the eye may occur simultaneously with the flash, but it would be impossible to foresee or prevent it. Such a coincidence however would be extremely rare.

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Fig. 2

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Fig. 3

Since the wink or reflex action does not occur until one-twelfth of a second after the flash has commenced, a flash powder that has an effective speed not slower than one-twelfth is sufficiently rapid for portraiture.

An objectionable effect seen in some flashlight work but not actually produced by the flash itself is what is known as the flashlight stare, so well reproduced in Figure 2. This is produced by another of nature's efforts to adapt herself to different conditions. Just as when the eye is subjected to a sudden increase in brightness it will close the iris and the eyelid to keep out the light, it will work the other way in darkness or when the illumination is reduced below normal. In the effort to see better at a lower level of illumination the iris becomes dilated and the eyelids and eyebrows raised.

Figure 3 was made almost immediately after Figure 2, the eyes being brought back to normal by pointing the light from an electric lamp at the face, and producing an illumination approximating weak daylight, which had the effect of contracting the dilated pupils and drawing down

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By H. V. Roberts Utica, N. Y.

The eyelids to their normal position, usually seen in ordinary daylight. A good light must be maintained until the moment of the flashlight exposure to prevent this stare and the eye must not be focused into any dark shadow. Care must also be taken that the shutter is not opened for any appreciable time before or after the flash in order to avoid a double image, made possible by the auxiliary light should there be any movement of the sitter or camera. Such a double image may be entirely prevented by the use of an arrangement which opens the camera shutter and sets off the flash at the same time.