Part 8 (1/2)
_Miscellaneous._--There are many interesting effects due to diffraction of light by edges of objects, by meshes such as a wire screen or a handkerchief, by the eye-media, etc. On looking at a very bright small light-source it may be seen to be surrounded by many colors.
Streamers of light appear to radiate from brilliant sources and all bright areas colored or colorless, when viewed amid dark surroundings, appear to be surrounded by diffuse brushes of light. These brushes are likely to be of a bluish tint.
Many of these phenomena are readily explained, but this cannot be done safely without knowing or recognizing all conditions. Many are not easily explained, especially when reported by others, who may not recognize certain important conditions. For example, authentic observers have reported that black letters on white paper appeared vivid red on a white background, under certain conditions. Of the latter, the apparently important one was ”sun's rays falling aslant the forehead.” When the eyes were shaded with the hand the letters immediately appeared black as they should.
The influence of the color of an object upon its apparent weight is relatively slight, but there is evidence of a tendency to judge a red or black object to be slightly heavier than a yellow or blue object of the same weight. It appears that hue is a minor factor in influencing the judgment and that there is no correlation between the affective quality of a color and its influence upon apparent weight. Although the scanty evidence available attributes but a slight influence to color in this respect, it is of interest in pa.s.sing as a reminder of the many subtle factors which are at work modifying our judgments.
X
LIGHTING
It should be obvious by this time that the lighting of objects or of a scene can alone produce an illusion, and that it can in still more cases contribute toward an illusion. Furthermore, there are many cases of illusions in lighting due to brightness and color. Many effects of lighting have been described elsewhere with detailed a.n.a.lyses of the underlying principles, but a condensed survey applying particularly to illusions will be presented here.
The comparison of intaglio with low relief has been mentioned several times in preceding chapters. Examples of these as related to lighting are found in Figs. 70 to 73. Fig. 70 represents a bas-relief lighted from above and Fig. 71 would ordinarily be taken to represent a bas-relief lighted from below. However, the latter was made from a photograph of the mold (intaglio) from which the bas-relief was made and Fig. 71 really represents an intaglio lighted from above.
Similarly Fig. 72 represents the bas-relief lighted from the left and Fig.
73 ordinarily would be taken to be a bas-relief lighted from the right.
However, Fig. 73 was made from a photograph of an intaglio lighted from the left. These amply demonstrate the effect of lighting as an influence upon the appearance of objects and they indicate the importance of correct a.s.sumptions in arriving at a correct judgment. In these cases the concealment of the light-source and the commonness of bas-relief as compared with intaglio are the causes for the illusion or the error in judgment. Certainly in these cases the visual sense delivers its data correctly.
[Ill.u.s.tration: Fig. 70.--A bas-relief lighted from above.]
[Ill.u.s.tration: Fig. 71.--An intaglio lighted from above.]
[Ill.u.s.tration: Fig. 72.--A bas-relief lighted from the left.]
[Ill.u.s.tration: Fig. 73.--An intaglio lighted from the left.]
[Ill.u.s.tration: Fig. 74.--_a._ A disk (above) and a sphere (below) lighted from overhead. _b._ A disk and a sphere lighted by perfectly diffused light.]
In Fig. 74 the upper object is a disk and the lower is a sphere. In _a_ Fig. 74 the lighting is due to a source of light of rather small physical dimensions directly above the objects. The same objects illuminated by means of highly diffused light (that is, light from many directions and of uniform intensity) appear as in _b_. Both objects now appear as disks. It is obvious that under appropriate lighting a disk might be taken for a sphere and vice versa, depending upon which dominates the judgment or upon the formulation of the attendant a.s.sumptions.
Incidentally an appearance quite similar to that of _a_, Fig. 74 is obtained when the light-source is near the observer; that is, when it lies near the line of sight.
[Ill.u.s.tration: Fig. 75.--A concave hemispherical cup on the left and a convex hemisphere on the right lighted by a light-source of large angle such as a window.]
Somewhat similar to the confusion of intaglio with bas-relief is the confusion of the two hemispherical objects ill.u.s.trated in Fig. 75. The one on the left is concave toward the observer. In other words, both could be hemispherical sh.e.l.ls--one a mold for the other. Under the lighting which existed when the original photographs were made they could both be taken for hemispheres. The lighting was due to a large light-source at the left, but if the object on the left is a.s.sumed (incorrectly) to be a hemisphere convex toward the observer or a sphere, it must be considered to be lighted from the right, which is also an incorrect a.s.sumption. Obviously, if the direction of the dominant light is clear to the observer, he is not likely to make the error in judgment. Incidentally the object on the right might be a.s.sumed to be a sphere because a sphere is more commonly encountered than a hemisphere.
[Ill.u.s.tration: Fig. 76.--The same as Fig. 75, but lighted by a very small light-source.]
The same objects are represented in Fig. 76 lighted from the left by means of a light-source of relatively small dimensions; that is, a source subtending a relatively small solid-angle at the objects. In this case the sharp shadow due to the edge of the hemispherical cup (on the left) is likely to cause the observer to inquire further before submitting his judgment. The more gradual modulation of light and shade as in the case of a sphere or a hemisphere convex toward the observer is not present in the case of the cup. This should be sufficient information for the careful observer to guide him, or at least to prevent him from arriving at the definite conclusion that the left-hand object is a hemisphere with its convex side toward him. Furthermore it should be noted that we often jump at the conclusion that an object is a sphere even though we see with one eye practically only a hemisphere and with two eyes hardly enough more to justify such a conclusion. However, spheres are more commonly encountered than hemispheres, so we take a chance without really admitting or even recognizing that we do.
The foregoing figures ill.u.s.trate several phases which influence our judgments and the wonder is that we do not make more errors than we do. Of course, experience plays a large part and fortunately experience can be depended upon in most cases; however, in the other cases it leads us astray to a greater extent than if we had less of it.
The photographer, perhaps, recognizes more than anyone else the pitfalls of lighting but it is unfortunate that he is not better acquainted with the fundamentals underlying the control of light. Improper lighting does produce apparent incongruous effects but adequately controlled it is a powerful medium whose potentiality has not been fully realized. The photographer aims to illuminate and to pose the subject with respect to the source or sources of light so that undesirable features are suppressed and desirable results are obtained.
Finally his work must be accepted by others and the latter, being human, possess (unadmittedly of course) a desire to be ”good looking.” Lighting may be a powerful flatterer when well controlled and may be a base revealer or even a creator of ugliness.
Incidentally, the photographer is always under the handicap of supplying a ”likeness” to an individual who perhaps never sees this same ”likeness” in a mirror. In other words, the image which a person sees of himself in a mirror is not the same in general that the photographer supplies him in the photographic portrait. The portrait can be a true likeness but the mirrored image in general cannot be. In the mirror there is a reversal of the parts from right to left. For example, a scar on the right cheek of the actual face appears on the left cheek in the mirror. Faces are not usually symmetrical and this reversal causes an individual to be familiar with his own facial characteristics in this reversed form. This influence is very marked in some cases. For example, suppose the left side of a companion's face to be somewhat paralyzed on one side due to illness. We have become more or less oblivious to the altered expression of the left side by seeing it so often. However, if we catch a glimpse of this companion's face in the mirror and the altered expression of the left side now appears upon the right side of the face, the contrast makes the fact very conspicuous. Perhaps this accounts for the difference which exists between the opinions of the photographer (or friends) and of the subject of the portrait.
All the illusions of brightness-contrast may be produced by lighting.