The photographic news

• Bandzählung: 29.1885
• Erscheinungsdatum: 1885
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: SLUB Dresden
• Rechtehinweis: Public Domain Mark 1.0
• URN: urn:nbn:de:bsz:14-db-id1780948042-188500006
• PURL: http://digital.slub-dresden.de/id1780948042-18850000
• OAI: oai:de:slub-dresden:db:id-1780948042-18850000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Bemerkung: Seite I-II fehlen in der Vorlage. Paginierfehler: Seite 160 als Seite 144 gezählt.
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

542 THE PHOTOGRAPHIC NEWS. [August 21, 1885. single B, is because it has a lower magnifying power. The opposite holds good in regard to all the other lenses. Their field is less because the makers have given them greater magnifying power than their low angle glasses of the same denomination. It is no doubt almost impossible to get a low angle and a wide angle quarter of the same power, but if such glasses could be procured, Mr. Skertchly would find the field of each of them the same. As another proof of this we put the Iris diaphragm on the microscope above the quarter object of lens by Wray of 130°, and reduced the aperture by the diaphragm till it was almost nil, and still the size of field remained the same. We examined the foot of the dung-fly in the same microscope with the A eye-piece, but none of the quarter- glasses mentioned above showed the foot, and the three next joints of the leg, except the Zeiss C j of 50%, which has the largest field and lowest angle. The reason of this is its low magnifying power. Powell and Lealand’s quarter of 90° showed the foot and two joints, while Mr. Wray’s quarter of 130 s only showed foot and one joint. Mr. Walmsley’s recent description of his process is exactly the method I have used for a long time in pro ducing photo-monographs. I have not, however, found it necessary to get glasses specially made and corrected for the actinic focus. I have about a dozen-and-a-half of object-glasses, from 4 inch to Powell and Lealand’s } new formula water immersion, all chosen for their good quali ties as micro-objectives simply. 'They are by Wray, Zeiss, Powell and Lealand, and I can with any of them produce a micro-photo negative with as sharp and delicate an image as when the object is seen in the microscope.— Yours, &c., W. Forgan. [l‘o Signor Bottone.] Dear Sir,—I have examined the French triplet with which you took a photograph of a dung-fly’s foot, and find, by measurement with the micrometer, that its magnifying power, in conjunction with an A eye-piece, was rather over 250 diameter. The photograph taken was identical with the one published as a supplement to the Photographic News in May last, and included the whole foot.—1 am, dear sir, yours very faithfully, 3, Danbury Terrace, Wallington. FRANCIS Carter. Aroceedings of Sotiettes. London and Provincial Photographic Association. A meeting of this Society was held on Thursday, the 13th inst., Mr. A. Haddon in the chair. Mr. W. K. Burton presented a copy of his “Modern Photo graphy,” latest edition, to the Society. Mr. W. Cobb drew attention to the quantity of bronze powder on wrappers used for packing gelatine of continental manufacture. He had been much troubled with spots in his plates, and upon examination found numerous particles on the gelatine. Brush ing each sheet before use removed the evil. Replying to Mr. Henderson, he said the spots were transparent, with a nucleus in the centre. Mr. Henderson should expect the spots to have been opaque, and absent in emulsion filtered through wash-leather. Mr. J. J. BRIGINSHAW explained the method of printing in bronze, and said no care was taken to keep the particles strictly on the design. Mr. Burton remarked that spots having black centres were often due to extraneous matter on the glass. Mr. Henderson agreed with the last speaker, and had found the spot to remain after the surrounding gelatine had been treated with a stream of hot water. Mr. Cobb had made an experimental batch, purposely adding bronze powder; the plates were riddled with spots. Mr. Henderson suggested a coating of melted paraffine as a protection to bronze surfaces, dragon’s blood being used for tinting if required.] Mr. W. H. Harrison had lately been over some large works where he was shown the process of colouring paraffine. It con sisted in mixing a coal tar dye with stearic acid, and adding this to melted paraffine. Mr. A. Cowan drew attention to the keeping properties of thymol in hot weather, and showed some emulsion containing half a grain of thymol per ounce, which had remained in a firm jelly for the last three months. Mr. Henderson had relinquished its use, believing it tended to reduce the silver. An ounce of emulsion would dissolve half a grain of thymol in alcohol, but more would not be soluble. Messrs. Debenham and Cowan used thymol, and had found no evil effects from its use. Mr. Henderson made an experiment to prove that silver iodide does not exist in the presence of excess of bromide. Two and a-half grains of silver nitrate were dissolved in one ounce of distilled water, and a small quantity of potassium iodide added thereto; an excess of potassium bromide was then added to dissolve the silver iodide. The experiment, however, was not wholly satisfactory, and will be repeated. Mr. Burton said that dissolving iodide of silver in bromide was distinctly different to converting it into bromide. Mr. Henderson contended that even if silver iodide is precipi tated in an emulsion it would, in all probability, be in a finer state of division ; otherwise, how was it that when a large quantity of iodide was used the plates fixed quicker than when only a little was present ? Referring to the Eastman paper containing glycerine to prevent curling in fixing and washing, and to be sure that such a film could be dried, he dissolved twenty grains of gelatine in an ounce of water, added an ounce of glycerine thereto, coated four or five plates, washed one for twelve hours, and put the others in the drying-box. After four days they were as moist as ever, but the washed plate was perfectly hard ; which showed that glycerine would wash out of a gelatine film, and certain gummy substances would do the same. These plates were passed round, and after some discussion anent colloid bodies passing out from a body of gelatine (the previous subject), interchange of silver haloids was again reverted to, the Chairman, Messrs. Burton, Cobb, Cowan, Debenham, and Henderson taking part. Mr. F. Cox was elected a member of the Association. Manchester Amateur Photographic Society. The usual monthly meeting was held on Tuesday evening last, in the Technical Schools, Princess Street, Mr. Robert Graham in the chair. Messrs. Alfred Wilson, William Herbert Norris, Frederick Hilton, and Robert B. Wilson were elected members. Mr. William Stanley, the Hon. Sec., made a few remarks descriptive of Warnerke’s sensitometer. Mr. Stanley exhibited nine plates of different makers which he had tested, and said he thought the Society would serve a good purpose by strongly recommending the manufacturers not to issue gelatine plates without the sensitometer number, as the statement, thirty or fifty times wet plate, was simply illusory and misleading. Mr. Robert Graham gave his experience in ascertaining the equivalent foci of double combination lenses, premising that although a want of knowledge of the question did not prevent the obtaining of the best photographs, it was an interesting point to be assured of the exact equivalent foci of their lenses, and, besides any attempts at enlargement or reduction in the camera, in exact proportions, by making use of the tables of enlargement given by various authorities, would result, to say the least, in much annoyance. Unfortunately, the equivalent foci of lenses were not always correctly stated, even by the best known makers, in their catalogues, and there were many other lenses in the market, about which purchasers could learn but very little with any degree of certainty. There are several methods of determining the equivalent foci of lenses, but the one which he had adopted was by comparing the size of the image projected on the focussing screen of the camera by the lens, whose equivalent focus it was desirous to know, with that of an image of the same object, from the same standpoint, received through a single lens of an exactly known focus. He had used a spectacle lens, guaranteed to him by an eminent firm of makers of these lenses, as being of ten inches solar focus, and as the equivalent focus of a lens was always in proportion to its magnifying power, it followed that if an image of a certain object given by the spectacle lens measured two inches, and that one inch was the size of an image of the same object received