Such is Mr. Wheatstone’s rule, for which he has assigned no reason whatever. In describing the binocular camera, in which the lenses must be only 2½ inches distant for portraits, I have shewn that the pictures which it gives are perfect representations of the original, and therefore pictures taken with lenses or cameras at any other distance, must be different from those which are seen by the artist looking at the sitter from his camera. They are, doubtless, both pictures of the sitter, but the picture taken by Mr. Wheatstone’s rule is one which no man ever saw or can see, until he can place his eyes at the distance of twenty inches! It is, in short, the picture of a living doll, in which parts are seen which are never seen in society, and parts hid which are always seen.
In order to throw some light upon his views, Mr. Wheatstone got “a number of Daguerreotypes of the same bust taken at a variety of different angles, so that he was enabled to place in the stereoscope two pictures taken at any angular distance from 2° to 18°, the former corresponding to a distance of about six feet, and the latter to a distance of about eight inches.” In those taken at 2°, (the proper angle,) there is “an undue elongation of lines joining two unequally distant points, so that all the features of a bust appear to be exaggerated in depth;” while in those taken at 18°, “there is an undue shortening of the same lines, so that the appearance of a bas-relief is obtained from the two projections of the bust, the apparent dimensions in breadth and height remaining in both cases the same.”
Although Mr. Wheatstone speaks thus decidedly of the relative effect produced by combining pictures taken at 2½° and 18°, yet in the very next paragraph he makes statements entirely incompatible with his previous observations. “When the optic axes,” he says, “are parallel, in strictness there should be no difference between the pictures presented to each eye, and in this case there would be no binocular relief, but I find that an excellent effect is produced when the axes are nearly parallel, by pictures taken at an inclination of 7° or 8°, and even a difference of 16° or 17° has no decidedly bad effect!”
That Mr. Wheatstone observed all these contradictory facts we do not doubt, but why he observed them, and what was their cause, is a question of scientific as well as of practical importance. Mr. Wheatstone was not aware[51] that the Daguerreotype pictures which he was combining, taken with large lenses, were not pictures as seen with two human eyes, but were actually binocular and multocular monstrosities, entirely unfit for the experiments he was carrying on, and therefore incapable of testing the only true method of taking binocular pictures which we have already explained.
Had Mr. Wheatstone combined pictures, each of which was a correct monocular picture, as seen with each eye, and as taken with a small aperture or a small lens, he would have found no discrepancy between the results of observation and of science. From the same cause, we presume, namely, the use of multocular pictures, Mr. Alfred Smee[52] has been led to a singular method of taking binocular ones. In one place he implicitly adopts Mr. Wheatstone’s erroneous rule. “The pictures for the stereoscope,” he says, “are taken at two stations, at a greater or less distance apart, according to the distance at which they are to be viewed. For a distance of 8 inches the two pictures are taken at angles of 18°, for 13 inches 10°, for 18 inches 8°, and for 4 feet 4°.” But when he comes to describe his own method he seems to know and to follow the true method, if we rightly understand his meaning. “To obtain a binocular picture of anybody,” he says, “the camera must be employed to take half the impression, and then it must be moved in the arc of a circle of which the distance from the camera to the point of sight[53] is the radius for about 2½ inches when a second picture is taken, and the two impressions conjointly form one binocular picture. There are many ways by which this result may be obtained. A spot may be placed on the ground-glass on which the point of sight should be made exactly to fall. The camera may then be moved 2½ inches, and adjusted till the point of sight falls again upon the same spot on the ground-glass, when, if the camera has been moved in a true horizontal plane the effect of the double picture will be perfect.” This is precisely the true method of taking binocular pictures which we had given long before, but it is true only when small lenses are used. In order to obtain this motion in the true arc of a circle the camera was moved on two cones which converged to the point of sight, and Mr. Smee thus obtained pictures of the usual character. But in making these experiments he was led to take pictures when the camera was in continual motion backwards and forwards for 2½ inches, and he remarks that “in this case the picture was even more beautiful than when the two images were superimposed!” “This experiment,” he adds, “is very remarkable, for who would have thought formerly that a picture could possibly have been made with a camera in continual motion? Nevertheless we accomplish it every day with ease, and the character of the likeness is wonderfully improved by it.” We have now left the regions of science, and have to adjudicate on a matter of opinion and taste. Mr. Smee has been so kind as to send me a picture thus taken. It is a good photograph with features enlarged in all azimuths, but it has no other relief than that which we have described as monocular.
A singular effect of combining pictures taken at extreme angles has been noticed by Admiral Lageol. Having taken the portrait of one of his friends when his eyes were directed to the object-glass of the camera, the Admiral made him look at an object 45°! to the right, and took a second picture. When these pictures were placed in the stereoscope, and viewed “without ceasing, turning first to the right and then to the left, the eyes of the portrait follow this motion as if they were animated.”[54] This fact must have been noticed in common stereoscopic portraits by every person who has viewed them alternately with each eye, but it is not merely the eyes which move. The nose, and indeed every feature, changes its place, or, to speak more correctly, the whole figure leaps from the one binocular position into the other. As it is unpleasant to open and shut the eyes alternately, the same effect may be more agreeably produced in ordinary portraits by merely intercepting the light which falls upon each picture, or by making an opaque screen pass quickly between the eyes and the lens, or immediately below the lens, so as to give successive vision of the pictures with each eye, and with both. The motion of the light reflected from the round eyeball has often a striking effect.
From these discussions, our readers will observe that the science, as well as the art of binocular portraiture for the stereoscope, is in a transition state in which it cannot long remain. The photographer who works with a very large lens chooses an angle which gives the least unfavourable results; his rival, with a lens of less size, chooses, on the same principle, a different angle; and the public, who are no judges of the result, are delighted with their pictures in relief, and when their noses are either pulled from their face, or flattened upon their cheek, or when an arm or a limb threatens to escape from their articulation, they are assured that nature and not art is to blame.
We come now to consider under what circumstances the photographer may place the lenses of his binocular camera at a greater distance than 2½ inches, or his two cameras at a greater angle than that which we have fixed.
1. In taking family portraits for the stereoscope, the cameras must be placed at an angle of 2° for 6 feet, when the binocular camera is not used.
2. In taking binocular pictures of any object whatever, when we wish to see them exactly as we do with our two eyes, we must adopt the same method.