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The photographic news
- Bandzählung
- 35.1891
- Erscheinungsdatum
- 1891
- Sprache
- Englisch
- Signatur
- F 135
- Vorlage
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- SLUB Dresden
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- Public Domain Mark 1.0
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- urn:nbn:de:bsz:14-db-id1780948042-189100009
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- http://digital.slub-dresden.de/id1780948042-18910000
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- oai:de:slub-dresden:db:id-1780948042-18910000
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- Bandzählung
- No. 1722, September 4, 1891
- Digitalisat
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The photographic news
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Band 35.1891
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618 THE PHOTOGRAPHIC NEWS. | September 4, 1891. is not hurried, process blocks give very wonderful results. But when such blocks have to be used for illustrated papers of which tens of thousands of copies have to be issued weekly, the time and care which it is necessary to give to these fine-grained, shallow blocks becomes an impossibility, and a blurred and generally faulty reproduction is too often the result. Of course there are exceptions, and we can point to many admirably printed pictures from such process blocks in our own leading illustrated journals; but, as a whole, they are not so satisfactory as the wood-cuts they have so much superseded. To answer the question which forms the title of this article. We do not think that photography will kill wood-engraving, and much as we have the interests of the former at heart, we most sincerely hope that wood engraving will always keep a forward position. It is certain that it will continue to hold its own with regard to sketches “from our special correspondent at the seat of war”; for such sketches are necessarily rough in their character, and invariably pass through the hands of a capable artist at home, who, from their somewhat vague outlines, draws a finished picture on the wood, which is afterwards engraved. In certain cases where the original drawing is of a more finished character, and is in line, the original is reproduced by process. Such a picture has always an additional interest attached to it, from being a fac simile of what the artist drew on the spot. PRICES OF RARE METALS. As some of the rare metals of the platinum group are attracting more or less attention for photographic purposes, the following list, with prices attached, will prove of interest. The rarest metal—and it is so rare that recent discoveries have thrown doubt on its elemental character—is didymium, and its present market price, if anyone may thus term the quotation of an article that never appears on the market, is 4,500 dollars per pound. The next costliest metal is barium, an element belonging to the alkaline earth group ; its value is 3,750 dollars. Beryllium, or glucinum, a metallic substance found in the beautiful beryl, is quoted at 3,275 dollars. Yttrium, a rare metal of the boron-aluminium group, so called because first noticed at Ytterby, in Sweden, is stated to be worth at present 2,250 dollars per pound. Niobium, or columbium, a name suggestive of the American origin of the metal, it having been first discovered in Connecticut, is valued to-day at 2,000 dollars per pound. The price of rhodium, an extremely hard and brittle substance, which owes its name to the rose-red colour of certain of its solutions, is also 2,000 dollars. Vanadium, deriving its title from one of the appella tions of the Scandinavian goddess, Freya, and at one time con sidered the rarest of metallic elements, has been reduced in price to 1,775 dollars, at which value there will, no doubt, be many eager buyers. Iridium, a very heavy metal of the platinum group, so named from the iridescence of some of its solutions, and well known in connection with its use for the points of gold pens, may be bought to-day at approximately 700 dollars per pound. Osmium, another metallic element of the platinum group, is hard, infusible, and the heaviest substance known ; its present value is 625 dollars per pound. Palladium, a silver-white, fusible metal used in the manufacture of certain parts of time-pieces, and occasionally applied in dentistry, is worth 500 dollars per pound. The present price of platinum, the better-known tin-white, ductile, but very infusible metal, is on a par with that of gold—viz., about 350 dollars per pound,—American Journal of Photography. PERSPECTIVE IN VISION, AND IN PHOTO- GRAPIIY. BY W. H. WHEELER. Some Effects of Plane Projection—Resources of Photography Greater than Artists suppose. In endeavouring to compare the perspective of natural vision with that of photography, we are met at the outset by the difference between the necessary conditions of a view depicted on a plane surface, such as a sensitive plate, from: First, the depth and solidity of nature; and secondly, the conditions of our visual sense and perception of it. We ought to know each of these sets of conditions before attempting really to compare them, and yet it is by com parison that their distinctive features become most striking. We will endeavour to point out those most important as we go on. Perhaps the process of copying from a rectangular original, which needs to be reproduced without distortion, to another true rectangle, is the one with whose conditions photographers are most generally familiar in this connection, and with which we propose to begin. We all know that for a straight and true reproduction of this kind, it is necessary—and, with a rectilinear lens, nothing else is absolutely necessary—that the planes of both the original and’ the copy be truly parallel to one another. For good optical definition it is well, too, if the line of sight, which should then also be the axis of the lens, is placed in a position perpendicular to both these planes, and also so as to join their centres ; though small differences are unimportant even for definition, and, as regards distortion, neither of these conditions are essential at all, whether with a lens or with a pinhole. But that the planes of original and copy be truly parallel to one another is absolutely essential; for then, and only then, all the lines from points in the original, passing through stop or pinhole to their corresponding points in the copy, bear strictly the same proportion to one another. The scale of reproduction is then the same all over, and the copy (provided the stop or pinhole be sufficiently small for good optical definition) will accurately reproduce the original in shape as well as in detail. Just so it is if we set up our camera exactly in front of a building. Provided our lens is rectilinear, and the plane of our picture parallel to the face of the building, both vertically and horizontally, we may tilt our camera until it points obliquely towards both the building and the sensitive plate; yet, provided the back is kept vertically and horizontally to this true parallelism, both vertical and horizontal lines will be parallel on the plate, just as they actually are on the building itself. Such a picture, it is true, will probably be too stiff and symmetrical to be either artistic or pleasing—that is another matter altogether—but it will be an accurate reproduction in form of the original, and the face of it will be true to scale. In such a case, photographic methods of measurement will certainly not be fallacious, nor will they mislead if, instead of tilting our camera and adjusting by the swing-back, we move a sliding front vertically or horizontally so as to bring our lens opposite a margin of the plate instead of its centre. Neither a central position for our lens, nor perpendicularity of the line of sight to the plane of the plate or of the building, are conditions that affect anything beyond accuracy of optical definition. The lines of any surface in the object which is parallel to the plane of the sensitive plate will always be reproduced in their true proportions.
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