agree. For instance, an angle of 15° is spoken of as being equivalent to the measurement 1 in 5. An angle of 10° is said, or implied, to be the same as 1 in 10. This is far from being the fact. According to my calculations, the following are the real equivalents:—
| An angle of | 15° | is equal to | 1 in 4. |
| " | 12° | " | 1 in 5. |
| " | 10° | " | 1 in 6. |
| " | 6½° | " | 1 in 9. |
| " | 6° | " | 1 in 10. |
| " | 5° | " | 1 in 12. |
| " | 4° | " | 1 in 15. |
Will any of your readers oblige me by solving the above anomalies, and by giving the proper angles or measurement under which objects should be taken when near, moderately distant, or far removed from the camera; stating, at the same time, at how many feet from the camera an object is to be considered as near, or distant, or between the two? It would be a great assistance to beginners in the stereoscopic art, if some experienced gentleman would state the best distances and angles for taking busts, portraits, groups, buildings, and landscapes.
It is said that stereoscopic pictures at great distances, such as views, should be taken "with a small aperture." But as the exact dimensions are not mentioned, it would be equally serviceable if, to the other details, were added some account of the dimensions of the apertures required for the several angles.
In the directions given in the work from which I have quoted, it is said that when pictures are taken with one camera placed in different positions, the angle should be 15°; but when taken with two cameras, the angle should be 10°. Is this right? And, if so, why the difference?
In the account given by you of Mr. Wilkinson's ingenious mode of levelling the cameras for stereoscopic pictures, it is said the plumb-line should be three feet long, and that the diagonal lines drawn on the ground glass should be made to cut the principal object focussed on the glass; and "when you have moved it, the camera, 8 or 10 feet, make it cut the same object again." At what distance is the object presumed to be?
Any information upon the above matters will be a great service, and consequently no slight favour conferred upon your constant reader since the photographic correspondence has been commenced.
φ.
Photographic Portraits of Criminals, &c.—Such experience as I have had both in drawing portraits and taking photographs, impels me to hint to the authorities of Scotland Yard that they will by no means find taking the portraits of gentlemen that are "wanted" infallible, and I anticipate some unpleasant mistakes will ere long arise. I have observed that inability to recognize a portrait is as frequent in the case of photographs as on canvass, or in any other way. I defy the whole world of artists to reduce the why and wherefore into a reasonable shape; one will declare that "either" looks as if the individual was going to cry; the next critic will say he sees nothing but a pleasant smile. "I should never have known who it is if you hadn't told me," says a third; the next says "it's his eyes, but not his nose;" and perhaps the next will say, "it's his nose, but not his eyes."
I was present not long since at the showing a portrait, which I think about the climax of doubt. "Not a bit like," was the first exclamation. The poor artist sank into his chair; after, however, a brief contemplation, "It's very like, in-deed; it's excellent:" this was said by a gentleman of the highest attainments, and one of the best poets of the day.