PHOTOGRAPHIC CORRESPONDENCE.
Mr. Lyte's Treatment of Positives.—It would be quite superfluous, after the very excellent communication of Mr. Pollock, were I to give a detailed account of my method of printing albumen positives, as, in the main, we both follow the process of Mr. Le Gray. But as we both have our own improvements on the original process, I will ask for space in which to record our differences in manipulation.
First, in regard to the chloride of gold, I always find, and I believe such is the experience of many photographers, that all salts of gold, though they heighten the effect at first, have a slow, but sure, destructive action on the picture.
Next, I find that acetic acid, by generating sulphurous acid, has a similar effect, and my care was to try and make a solution which should be free from these defects. I first take my positive, which, as a general rule, I print at least half as dark again as the shade required. This done, I wash it well with water, and next with salt and water in the proportion of about half a grain per gallon, or quite a tasteless solution; this removes all the nitrate of silver from the paper, or if there is any left, the bath of salt decomposes it, leaving none in the texture of the paper to unite with the hypo., which otherwise forms a sticky substance, difficult to remove, which may be readily seen on looking through a positive which has been too hastily finished in the usual way, giving a dark shade, and a want of transparency to the lights. I then place the picture in a bath composed as follows:
Sodæ hyposul. 3 oz.
Argent. chlorid. 70 grs.
Potassii iodidi 5 grs.
Pyrogallic acid 1½ to 2 grs.
The iodide of potassium I add on the same principle as Mr. Pollock's iodide of silver, but as being
more convenient, as immediately on being added it decomposes some of the chloride of silver, and forms iodide of silver. I am happy to find that Mr. Pollock confirms me in the use of this salt; which I had long thought to improve the tone of my pictures. The liquid, which will become rapidly very dark coloured, must be set aside in an open vessel in a warm place for some weeks, e.g. till, when a positive is placed in it, left for a short time, and then washed with water, it shows clean and not mottled in the light. The solution may be kept always exposed, and much improves by this: if much used, it should be replenished with a simple solution of hypo. three ounces or two ounces to the pint; if little used, it may be filled up as much as evaporates with pure water.
The positive is left in this solution till the required tint is obtained, when it is to be placed in plain hypo. two ounces to the pint, and in about a quarter of an hour transferred to a basin of pure water, and well washed in several waters. The other detail of Mr. Pollock's process is so admirably and clearly given, and so like that I pursue, that I will not trouble your columns with it again.
The after-bath of pure hypo. is not absolutely necessary; and where it is desired to obtain fine olive, and dark sepia, and black tints, a better tone results from washing well, long, and frequently, with water alone.
This bath also gives very rich tints with paper, prepared without albumen: viz.—
Chloride of ammonium 5 grs.
Water 1 oz.
Lay the paper on this, and then hang it up to dry, and excite with ammonio-nitrate containing seventy grains of nitrate of silver to one ounce of water. Should the above solution not give the requisite tints soon after being made, add more chloride of silver; but bear in mind that the solution will then soon become saturated when setting positives, and when this occurs it must be rectified by the addition of a small portion of fresh hypo. alone.
F. Maxwell Lyte.
P.S.—I may add that I have only lately tried the addition of the iodide of potassium to my setting liquid, and so must qualify my recommendation of it by saying so.
Florian, Torquay.
Stereoscopic Angles.—I am obliged to Messrs. Shadbolt and Wilkinson for the information given in reply to my Queries (Vol. vii., p. 505.) My mode of operation is precisely that of Mr. Wilkinson: "I obtain all the information I can from every source; then try, and judge for myself." Hence the present letter.
I regret to be obliged to differ from Mr. Shadbolt, but there is a point in his communication which appears to me to arise from a misconception of the stereoscopic problem. He says (p. 557.), "for distant views there is in nature scarcely any stereoscopic effect." Now, surely visual distance is merely visual stereosity; for, to see an object solid is merely to see its parts in relief, some of them appearing to project or recede from the others. It is the difficulty of producing this effect in landscapes, by the ordinary camera process, that renders views taken by such means so deficient in air, or, as the artists term it, aerial perspective, most distant objects seeming almost as near as those in the foreground. This indeed is the main defect of all photographs: they are true representations of nature to one eye—cyclopean pictures, as it were—appearing perfectly stereoscopic with one eye closed, but seeming absolutely flattened when viewed by the two eyes. I remember being shown a huge photograph of the city of Berlin, taken from an eminence; and a more violent caricature of nature I never set eyes upon. It was almost Chinese in its perspective: the house-tops appeared to have been mangled. It was a wonderful work of art, photographically considered; but artistically it was positively hideous. But the same defect exists in all monophotographic representations, though in a less degree, and consequently less apparent than in views to which a sense of distance is essential. In portraits, the features appear slightly flattened; and until photographers are able to overcome this, the chief of all obstacles to perfection, it is idle to talk of the art giving a correct rendering of nature. This is what is wanted, more than colour, diactinic lenses, multiplication of impressions, or anything else. And when it is remembered that the law of an ordinary convex lens is, the farther the object from the lens the nearer the focus, and, vice versâ, the nearer the object the farther the focus, it becomes evident that by such an instrument distant objects must be made to appear near, and near objects distant, and nature consequently mangled.
The stereoscope gives us the only demonstrably correct representation of nature; and when that instrument is rendered more simple, and the peep-show character of the apparatus disconnected from it, the art of photography will transcend the productions of the painter—but not till then.
I am anxious to obtain all the information I can from such of your photographic readers as are practically acquainted with the stereoscopic portion of the art relative to the angles under which they find it best to take their pictures for given distances.
Mr. Fenton, the secretary of the Photographic Society, takes his stereoscopic pictures, when the objects are 50 feet and upwards from the camera, at 1 in 25. This is, as Mr. Shadbolt states, Professor Wheatstone's rule for distances.
Mr. Wilkinson, on the other hand, asserts that 3 feet in 300 yards is sufficient separation for the cameras: this is only 1 in 300,—a vast difference truly.
"For views across the Thames," says the editor of the Photographic Journal, "the cameras should be placed 12 feet apart, and with this separation the effect is declared to be astonishing."
Mr. Wilkinson, however, asserts that from 4 to 6 feet in a mile will do well enough!
Farther, Mr. Latimer Clark (the inventor of an ingenious stereoscopic camera) states that with regard to the distance between the two positions of the cameras, he knows no good reason why the natural distance of the eyes, viz. 2½ inches, should be much exceeded. "A little extra relief is obtained," he adds, "without visible distortion, by increasing the separation to about 4 or 5 inches; but if this distance be greatly exceeded, especially for near objects (I give the gentleman's own words), they become apparently diminished in size, and have the appearance of models and dolls rather than natural objects."
The reason for making the separation between the cameras greater than that between the two eyes, is exceedingly simple. The stereograph is to be looked at much nearer than the object itself, and consequently is to be seen under a much larger angle than it is viewed by the two eyes in nature. Hence the two pictures should be taken at the angle under which they are to be observed in the stereoscope. Suppose the object to be 50 feet distant, then of course it is seen by the two eyes under an angle of 2½ inches in 50 feet, or 1 in 240. But it is intended that the stereograph should be seen by the two eyes when but a few inches removed from them, or generally under an angle of 2½ in 12 inches, or nearly 1 in 5. Hence it is self-evident that the stereoscopic angle should be considerably larger than that formed by the optic axes of the two eyes when directed to the object itself.
But there is great diversity of opinion as to the extent of the angles requisite for producing the precise stereoscopic or distantial effect of nature. For myself I prefer Professor Wheatstone's rule, 1 in 25 for objects beyond 50 feet distant. For portraits I find the best angle 1 in 10 when the sitter is 10 feet off, and for busts about 1 in 5 when placed about 5 or 6 feet from the cameras. But I should be happy to receive information from any of your readers concerning this important branch of the photographic art. For months past I have been engaged in a series of experiments in connexion with the subject, and wish for larger experience than it is possible for any single operator to acquire for himself.
Mr. Fenton, I may observe, does not keep the cameras parallel in taking landscapes, but inclines them so that the same object may occupy as nearly as possible the centre of the ground glass plate.
Nor is it essential that perfect horizontality or parallelism of the cameras should be maintained in copying trees. For buildings, however, it is absolutely necessary that the cameras be kept straight.
I am sorry thus to trespass on your space, but being anxious, as Mr. Wilkinson says, to collect information from every source, and your periodical being a happy medium for conveying and receiving instruction, I am glad to avail myself of such a channel.
Φ. (2)
P.S.—Mr. Claudet has, I perceive, been awarded the prize given by the Society of Arts for the best essay on the stereoscope. Can you, or any of your readers, inform me whether this is likely to be published, and when and at what price?
Query respecting Mr. Pollock's Process.—In Mr. Pollock's directions for obtaining positives which appeared in "N. & Q." (Vol. vii, p. 581.), iodide of silver is to be dissolved in a saturated solution of hypo. Can you give me the quantity of iodide of silver to be dissolved, and the quantity of the saturated solution of hypo. in which it is to be dissolved?
N. T. B.
Gallo-nitrate of Silver.—Can you inform me what the true nature of the decomposition is which takes place after a short time in the gallo-nitrate solution of silver? and if there be any ready means of rendering the silver it contains again available for photographic use?
Sir W. Newton, in the description of his calotype process, says: "Bring out with the saturated solution of gallic acid, and when the subject begins to appear, add the aceto-nitrate of silver solution." Which way of doing this is the best,—mixing the two solutions together and applying them to the paper; or applying the paper, when wetted with the gallic acid, to the silver solution?
T. L.