Naturalistic Photography for Students of the Art.

by P. H. Emerson

Fechner’s law.

In order to understand to what conclusions this leads, I must first explain the law which Fechner discovered for the scale of sensitiveness of the eye, which is a particular case of the more general psycho-physical law of the relations of the various sensuous impressions to the irritations which produce them. This law may be expressed as follows:—Within very wide limits of brightness, differences in the strength of light are equally distinct, or appear equal in sensation, if they form an equal fraction of the total quantity of light compared.

Thus, for instance, differences in intensity of one-hundredth of the total amount can be recognized without great trouble, with very different strengths of light, without exhibiting material differences in the certainty and facility of the estimate, whether the brightest daylight, or the light of a good candle be used.”

Herein, then, are contained the limits with which we can work, and the physiological reasons why we can render a fairly true impression of a scene in nature.

The only constant factor, then, is the ratio of luminous intensities,—that is, the picture must be as true as possible in relative tones or values. Obviously a picture of bright sunlight should look brighter in a moderately lighted room than the surrounding room, that is, its first impression on the observer should be as if he were looking at a landscape beyond the walls, through the frame.

From these remarks it will be seen how utterly impossible it is to render truly a bright sunlight scene, for if the values be true, starting from the top of the scale, the highest light, when you get to the middle tints, they are too black already, and the picture is out of tone and false. Obviously the right way is to start from the lower end of the scale, the darks, and get them as true as possible, and let the lights take care of themselves; but more of this anon.

D. Colour.

Colour.

As photographers, the matter of colour exercises us but indirectly, still the subject should be understood, on account of its bearing on painting. “Colour perception” says Le Conte, “is a single perception, and irresolvable with any other. It must, therefore, have its basis in retinal structure.”

Helmholtz divides the vibrations of ether known as light into three degrees. He says the longest and shortest rays do not essentially differ in any other physical property, except that we distinguish them from the intermediate waves.”[waves.”] Thus the ear can receive at once many waves of sound or notes, and they remain distinct, but notes of colour do not keep distinct in the same way, “so that the eye is capable of recognizing few differences in quality of light,” says Helmholtz, and can only perceive the elementary sensation of colour by artificial preparation. He also says, the only bond between the objective and subjective phenomena of colour may be stated as a law thus, “Similar light produces under like conditions a like sensation of colour. Light, which under like conditions, excites unlike sensations of colour is dissimilar;” what we want in art, then, is the appearance of the phenomena. The illumination of the sun’s rays cannot be weakened without at the same time weakening their heating and chemical action; this is a point to be remembered in exposure.