Naturalistic Photography for Students of the Art.

by P. H. Emerson

Fatigue weakens the apparent illumination of the entire field of vision.

The colour of illumination of a picture, too, varies greatly by effect of local colour.

What is constant in the colour of an object is not the brightness and colour of the light which it reflects, but the relation between the intensity of the different-coloured constituents of this light, on the one hand, and that of the corresponding constituents of the light which illuminates it on the other. For example, white paper in full moonlight is darker than black satin in daylight, or a dark object with the sun shining on it reflects light of exactly the same colour, and perhaps the same brightness, as a white object in shadow. Grey in shadow looks like white.

Brightness of local colour diminishes with the illumination or as the fatigue of the retina is increased. In sunshine, local colours of moderate brightness approach the brightest, whereas in moonlight they approach the darkest. Pictures to be seen in daylight do not admit of difference of brightness between sun and moon. As colours increase in brightness, red and yellow become apparently stronger than blue. Painters make yellow tints predominate when representing landscape in full sunshine, while moonlight scenes are blued. Helmholtz says:—“Differences of colour which are actually before our eyes are more easily apprehended than those which we only keep in memory, and contrast between objects which are close to one another in the field of vision are more easily recognized than when they are at a distance. All this contributes to the effect. Indeed, there are a number of subordinate circumstances affecting the result which it would be very interesting to follow out in detail, for they throw great light upon the way in which we judge of local colour; but we must not pursue the inquiry further here. I will only remark that all these effects of contrast are not less interesting for the scientific painter than for the physiologist, since he must often exaggerate the natural phenomenon of contrast in order to produce the impression of greater varieties of light and greater fulness of colour than can be actually produced by artificial pigments.”

Again, when turbidity is composed of fine particles its appearance is blue, as the mists seen in autumn hanging round coverts, but it is whiter than the aërial blue because of the colour of the covert behind. When this turbidity is absent the colours are brighter, hence the fierce blue on bright sunshiny days with easterly winds. This matter of turbidity must not be forgotten in portrait work; it is this which helps to give relief, hence the absurdity of all photographers' devices, the object of which is to minimize this turbidity. In addition to these is the ever-changing effect of atmosphere on colour, that subtle medium with which the enchantress Nature produces ever-changing effects, and its chief effect on colour is to lower it in brightness. Atmosphere greys all things, hence on a misty day all the colours are greyed—we have, in fact, a “grey day.”

Another point which must not be forgotten is that with bright illumination bright objects become more like the brightest, and with feeble illumination dark objects become more like the darkest. This is a very important matter, for it means that in bright sunshine the lightest greys are lost in white, whilst in dull weather the darkest greys are lost in black, hence the falsity of having deep blacks in brightly-lighted landscapes, and as has been shown, these are untrue, and the result of ignorance and of faulty manipulation. As Helmholtz has it, “The difference of brightness and not absolute brightness; and that the differences in them in this latter respect can be shown without perceptible incongruity if only their graduations are imitated with expression.”

E. Binocular Vision—Psychological Data.

Single Image.

Binocular Vision.

The remarks already made would apply equally well to man if he were a one-eyed animal, but we find there are other considerations to take into account since man is two-eyed. Now the phenomena of binocular vision cannot be treated of with such accuracy as the physical and physiological facts already discussed. In this subject we shall follow Le Conte. It is obvious there is a common binocular field of view for the two eyes. Now Dr. Le Conte shows us that we see all objects double, except under certain conditions. When we look directly at anything, then we see it clearly, but all things nearer to us than the object looked at and beyond it, are seen double, or blurred and indistinct. This is the case in life, as can be proved.