—— Rectory, Hereford.
PHOTOGRAPHIC CORRESPONDENCE.
Stereoscopic Queries.—Can any of your readers inform me what are the proper angles under which stereoscopic pictures should be taken?
Mr. Beard, I am informed, takes his stereoscopic portraits at about 6½°, or 1 in 9; that is to say, his cameras are placed 1 inch apart for every 9 inches the sitter is removed from them. The distance of the sitter with him is generally, I believe, 8 feet, which would give 10⅔ inches for the extent of the separation between his cameras. More than this has the effect, he says, of making the pictures appear to stand out unnaturally; that is to say, if the cameras were to be placed 12 inches apart (which would be equal to 1 in 8), the pictures would seem to be in greater relief than the objects.
I find that the pictures on a French stereoscopic slide I have by me have been taken at an angle of 10°, or 1 in 6. This was evidently photographed at a considerable distance, the triumphal arch in the Place de Carousel (of which it is a representation) being reduced to about 1¼ inch in height. How comes it then that the angle is here increased to 10° from 6½°, or to 1 in 6 from 1 in 9.
Moreover, the only work I have been able to obtain on the mode of taking stereoscopic pictures, lays it down that all portraits, or near objects, should be taken under an angle of 15°, or, as it says, 1 in 5; that is, if the camera is 20 feet from the sitter, the distance between its first and second position (supposing only one to be used) should not exceed 4 feet: otherwise, adds the author, "the stereosity will appear unnaturally great."
When two cameras are employed, the instructions proceed to state that the distance between them would be about 1/10th of the distance from the part of the object focussed. The example given is a group of portraits, and the angle, 1 in 10, is afterwards spoken of as being equivalent to an arc of 10°.
Farther on, we are told that "the angle should be lessened as the distance between the nearest and farthest objects increase. Example: if the farthest object be twice as far from the camera as the near object, the angle should be 5° to a central point between these two.
Now, I find by calculation that the measurements and the angle here mentioned by no means