Fig. 46.

Since the publication in 1849 of my description of the binocular camera, a similar instrument was proposed in Paris by a photographer, M. Quinet, who gave it the name of Quinetoscope, which, as the Abbé Moigno observes, means an instrument for seeing M. Quinet! I have not seen this camera, but, from the following notice of it by the Abbé Moigno, it does not appear to be different from mine:—“Nous avons été à la fois surpris et très-satisfait de retrouver dans le Quinetoscope la chambre binoculaire de notre ami Sir David Brewster, telle que nous l’avons décrite après lui il y a dix-huit mois dans notre brochure intitulée Stéréoscope.” Continuing to speak of M. Quinet’s camera, the Abbé is led to criticise unjustly what he calls the limitation of the instrument:—“En un mot, ce charmant appareil est aussi bien construit qu’il peut être, et nous désirons ardemment qu’il se répand assez pour récompenser M. Quinet de son habileté et de ses peines. Employé dans les limites fixées à l’avance par son véritable inventeur, Sir David Brewster; c’est-à-dire, employé à reproduire des objets de petite et moyenne grandeur, il donnera assez beaux résultats. Il ne pourra pas servir, evidemment, il ne donnera pas bien l’effet stéréoscopique voulu, quand on voudra l’appliquer à de très-grands objets, on a des vues ou pay sages pris d’une très-grande distance; mais il est de la nature des œuvres humaines d’être essentiellement bornées.”[47] This criticism on the limitation of the camera is wholly incorrect; and it will be made apparent, in a future part of the Chapter, that for objects of all sizes and at all distances the binocular camera gives the very representations which we see, and that other methods, referred to as superior, give unreal and untruthful pictures, for the purpose of producing a startling relief.

In stating, as he subsequently does, that the angles at which the pictures should be taken “are too vaguely indicated by theory,”[48] the Abbé cannot have appealed to his own optical knowledge, but must have trusted to the practice of Mr. Claudet, who asserts “that there cannot be any rule for fixing the binocular angle of camera obscuras. It is a matter of taste and artistic illusion.”[49] No question of science can be a matter of taste, and no illusion can be artistic which is a misrepresentation of nature.

When the artist has not a binocular camera he must place his single camera successively in such positions that the axis of his lens may have the directions EL, EL′ making an angle equal to LCL′, the angle which the distance between the eyes subtends at the distance of the sitter from the lenses. This angle is found by the following formula:—

Tang. ½A = ½d = 1.25
dd

d being the distance between the eyes, D the distance of the sitter, and A the angle which the distance between the eyes, = 2.5, subtends at the distance of the sitter. These angles for different distances are given in the following table:—

D = Distance of Camera
from the Sitter.		 A = Angle formed by the two
directions of the Camera.
5inches,28° 6′
6,2332
7,2014
8,1746
9,1548
10,1415
11,13 0
12,1 foot,1154
13,11 0
14,1017
15, 932
16, 856
17, 824
18, 756
19, 731
20, 710
24,2 feet, 558
30, 446
36,inches, 3 feet, 359
42, 325
48,4 feet, 259
54, 239
60,5 feet, 223
72,6 feet, 159
84,7 feet, 142
96,8 feet, 130
108,9 feet, 120
120,10 feet, 112

The numbers given in the greater part of the preceding table can be of use only when we wish to take binocular pictures of small objects placed at short distances from cameras of a diminutive size. In photographic portraiture they are of no use. The correct angle for a distance of six feet must not exceed two degrees,—for a distance of eight feet, one and a half degrees, and for a distance of ten feet, one and a fifth degree. Mr. Wheatstone has given quite a different rule. He makes the angle to depend, not on the distance of the sitter from the camera, but on the distance of the binocular picture in the stereoscope from the eyes of the observer! According to the rule which I have demonstrated, the angle of convergency for a distance of six feet must be 1° 59′, whereas in a stereoscope of any kind, with the pictures six inches from the eyes, Mr. Wheatstone makes it 23° 32′! As such a difference is a scandal to science, we must endeavour to place the subject in its true light, and it will be interesting to observe how the problem has been dealt with by the professional photographer. The following is Mr. Wheatstone’s explanation of his own rule, or rather his mode of stating it:—

“With respect,” says he, “to the means of preparing the binocular photographs, (and in this term I include both Talbotypes and Daguerreotypes,) little requires to be said beyond a few directions as to the proper positions in which it is necessary to place the camera in order to obtain the two required projections.

“We will suppose that the binocular pictures are required to be seen in the stereoscope at a distance of eight inches before the eyes, in which case the convergence of the optic axes is about 18°. To obtain the proper projections for this distance, the camera must be placed with its lens accurately directed towards the object successively in two points of the circumference of a circle, of which the object is the centre, and the points at which the camera is so placed must have the angular distance of 18° from each other, exactly that of the optic axes in the stereoscope. The distance of the camera from the object may be taken arbitrarily, for so long as the same angle is employed, whatever that distance may be, the picture will exhibit in the stereoscope the same relief, and be seen at the same distance of eight inches, only the magnitude of the picture will appear different. Miniature stereoscopic representations of buildings and full-sized statues are, therefore, obtained merely by taking the two projections of the object from a considerable distance, but at the same time as if the object were only eight inches distant, that is, at an angle of 18°.”[50]