The stereoscope

by David Brewster

In the beautiful combination of lenticular stereoscopes, which was exhibited by Mr. Claudet, Mr. Williams, and others, in the Paris Exhibition, and into which six or eight persons were looking at the same time, binocular pictures of a larger size could not have been conveniently used.

But, independently of these reasons, the question of large pictures has been practically settled. No such pictures are taken by the Daguerreotypists or Talbotypists, who are now enriching art with the choicest views of the antiquities, and modern buildings, and picturesque scenery of every part of the world; and even if they could be obtained, there are no instruments fitted for their exhibition. In the magnificent collection of stereoscopic pictures, amounting to above a thousand, advertised by the London Stereoscopic Company, there are no fewer than sixty taken in Rome, and representing, better than a traveller could see them there, the ancient and modern buildings of that renowned city. Were these sixty views placed on the sides of a revolving polygon, with a stereoscope before each of its faces, a score of persons might, in the course of an hour, see more of Rome, and see it better, than if they had visited it in person. At all events, those who are neither able nor willing to bear the expense, and undergo the toil of personal travel, would, in such a panorama,—an analytical view of Rome,—acquire as perfect a knowledge of its localities, ancient and modern, as the ordinary traveller. In the same manner, we might study the other metropolitan cities of the world, and travel from them to its river and mountain scenery,—admiring its noble castles in our descent of the Rhine,—its grand and wild scenery on the banks of the Mississippi, or the Orinoco,—the mountain gorges, the glaciers, and the peaks of the Alps and the Ural,—and the more sublime grandeur which reigns among the solitudes of the Himalaya and the Andes.

The following general rule for taking and combining binocular pictures is the demonstrable result of the principles explained in this chapter:—

Supposing that the camera obscura employed to take binocular portraits, landscapes, &c., gives perfect representations of them, the relief picture in the stereoscope, produced by their superposition and binocular union, will not be correct and truthful, unless the dissimilar pictures are placed in the stereoscope at a distance from the eyes, equal to the focal distance, real or equivalent, of the object-glass or object-glasses of the camera, and, whatever be the size of the pictures, they will appear, when they are so placed, of the same apparent magnitude, and in the same relief, as when they were seen from the object-glass of the camera by the photographer himself.

CHAPTER X.
APPLICATION OF THE STEREOSCOPE TO PAINTING.

Having explained the only true method of taking binocular portraits which will appear in correct relief when placed in the stereoscope, we shall proceed in this chapter to point out the application of the stereoscope to the art of painting in all its branches. In doing this we must not forget how much the stereoscope owes to photography, and how much the arts of design might reasonably expect from the solar pencil, when rightly guided, even if the stereoscope had never been invented.

When the processes of the Daguerreotype and Talbotype, the sister arts of Photography, were first given to the world, it was the expectation of some, and the dread of others, that the excellence and correctness of their delineations would cast into the shade the less truthful representations of the portrait and the landscape painter. An invention which supersedes animal power, or even the professional labour of man, might have been justly hailed as a social blessing, but an art which should supersede the efforts of genius, and interfere with the exercise of those creative powers which represent to us what is beautiful and sublime in nature, would, if such a thing were possible, be a social evil.

The arts of painting, sculpture, and architecture have in every age, and in every region of civilisation, called into exercise the loftiest genius and the deepest reason of man. Consecrated by piety, and hallowed by affection, the choicest productions of the pencil and the chisel have been preserved by the liberality of individuals and the munificence of princes, while the palaces of sovereigns, the edifices of social life, the temples of religion, the watch-towers of war, the obelisks of fame, and the mausolea of domestic grief, stand under the azure cupola of heaven, to attest by their living beauty, or their ruined grandeur, the genius and liberality which gave them birth. To the cultivation and patronage of such noble arts, the vanity, the hopes, and the holiest affections of man stand irrevocably pledged; and we should deplore any invention or discovery, or any tide in the nation’s taste, which should paralyse the artist’s pencil, or break the sculptor’s chisel, or divert into new channels the genius which wields them. But instead of superseding the arts of design, photography will but supply them with new materials,—with collections of costume,—with studies of drapery and of forms, and with scenes in life, and facts in nature, which, if they possess at all, they possess imperfectly, and without which art must be stationary, if she does not languish and decline.

Sentiments analogous to these have been more professionally expressed by M. Delaroche, a distinguished French artist,—by Sir Charles Eastlake, whose taste and knowledge of art is unrivalled,—and by Mr. Ruskin, who has already given laws to art, and whose genius is destined to elevate and to reform it. M. Delaroche considers photography “as carrying to such perfection certain of the essential principles of art, that they must become subjects of study and observation, even to the most accomplished artist.”... “The finish of inconceivable minuteness,” he says, “disturbs in no respect the repose of the masses, nor impairs in any way the general effect.... The correctness of the lines, the precision of the forms in the designs of M. Daguerre, are as perfect as it is possible they can be, and yet, at the same time, we discover in them a broad and energetic manner, and a whole equally rich in hue and in effect. The painter will obtain by this process a quick method of making collections of studies, which he could not otherwise procure without much time and labour, and in a style very far inferior, whatever might be his talents in other respects.” In the same spirit, Mr. Ruskin[58] considers “the art of photography as enabling us to obtain as many memoranda of the facts of nature as we need;” and long before Mr. Talbot taught us to fix upon paper the pictures of the camera obscura, the Rev. John Thomson, one of the most distinguished of our Scottish landscape painters, studied, in one of these instruments, the forms and colours of the scenes which he was to represent. Other artists, both in portrait and in landscape, now avail themselves of photography, both as an auxiliary and a guide in their profession; but there are certain difficulties and imperfections in the art itself, and so many precautions required in its right application, whether we use its pictures single, as representations on a plane, or take them binocularly, to be raised into relief by the stereoscope, that we must draw from the principles of optics the only rules which can be of real services to the arts of design.

In painting a landscape, a building, a figure, or a group of figures, the object of the artist is to represent it on his canvas just as he sees it, having previously selected the best point of view, and marked for omission or improvement what is not beautiful, or what would interfere with the effect of his picture as a work of high art. His first step, therefore, is to fix upon the size of his canvas, or the distance at which the picture is to be seen, which determines its size. His own eye is a camera obscura, and the relation between the picture or image on its retina is such, that if we could view it from the centre of curvature of the retina, (the centre of visible direction,) a distance of half an inch, it would have precisely the same apparent magnitude as the object of which it is the image. Let us now suppose that the artist wishes to avail himself of the picture in the camera obscura as received either on paper or ground-glass, or of a photograph of the scene he is to paint. He must make use of a camera whose focal length is equal to the distance at which his picture is to be seen, and when the picture thus taken is viewed at this distance (suppose two feet) it will, as a whole, and in all its parts, have the same apparent magnitude as the original object. This will be understood from [Fig. 47], in which we may suppose H to be the lens of the camera, RB the object, and Hy′ the distance at which it is to be viewed. The size of the picture taken with a lens at H, whose focal length is Hy′, will be b′r′, and an eye placed at H will see the picture b′r′ under an angle b′Hr′, equal to the angle RHB, under which the real object RB was seen by the artist from H. In like manner, a larger picture, byr, taken by a camera the focal distance of whose lens at H is Hy, will be an accurate representation of the object RB, when viewed from H, and of the same apparent magnitude. If either of these pictures, b′r′ or br, are viewed from greater or less distances than Hy′, or Hy, they will not be correct representations of the object RB, either in apparent magnitude or form. That they will be of a different apparent magnitude, greater when viewed at less distances than Hy′, Hy, and less when viewed at greater distances, is too obvious to require any illustration. That they will differ in form, or in the relative apparent size of their parts, has, so far as I know, not been conjectured. In order to shew this, let us suppose a man six feet high to occupy the foreground, and another of the same size to be placed in the middle distance, the distance of the two from the artist being ten and twenty feet. The apparent magnitudes of these two men on the photograph will be as two to one; and if we look at it at any distance greater or less than the focal length Hy′ of the lens, the same proportion of two to one will be preserved, whereas if we look at the original figures at a greater or less distance from them than the place of the artist, the ratio of their apparent magnitudes will be altered. If the artist, for example, advances five feet, the nearest man will be five feet distant and the other fifteen feet, so that their apparent magnitude will now be as three to one.