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The photographic news
- Bandzählung
- 24.1880
- Erscheinungsdatum
- 1880
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1145, August 13, 1880
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Zeitschrift
The photographic news
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Band 24.1880
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- Register Index 631
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Band
Band 24.1880
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Avu 61 13, 1880.] THE PHOTOGRAPHIC NEWS. 385 Ue Pqotograpbir Lehs, August 13, 1880. PHOTOGRAPHY IN AND OUT OF THE STUDIO. TIUNDERSTORSIS and GELATINO-BEOMIDE Work—Commer cial Plates—A Magic Lantern and Six Slides for Threepence Halfpenny—Distortion of Lenses by Pressure or Stain. Thunderstorms and Gclatino-Bromide Work.—Now that the capabilities of the gelatino-bromide process as a tho roughly practicable working method have been fully demonstrated, every circumstance which tends towards difficulty or uncertainty demands a most careful and ex haustive study. Several emulsion workers of experience have noticed that occasionally their labours have proved futile when the emulsion has been prepared, or has been kept in the liquid state, during a thunder-storm. Emul sion prepared under the circumstances referred to has been found to occasionally yield plates which proved to give foggy or veiled images, and to show all the signs of inci pient putrefaction having commenced in the gelatine. The i lea of atmospheric electricity influencing the results of emulsion work has, on the other hand, been ridiculed by some workers who have obtained excellent results with emulsion prepared during very violent thunderstorms. It is, in the first place, a tolerably well-established fact that an electrical discharge passed through an organic sub stance will sometimes very much increase any tendency which it may have to putrefy or decay. As an instance of this, we may mention the well-known fact that bodies of animals which have been killed by lightning decompose with extreme rapidity, and the notion that beer or milk often becomes sour during a thunderstorm may, perhaps, be something more than a domestic superstition. In con nection with this subject it must be remembered that an electric discharge always produces a series of induction currents in all conducting bodies within its sphere of action, these induction discharges, when arising from a flash of lightning, being generally known as return shocks; and there are many cases on record of men and other animals having been killed by these secondary elec trical disturbances. It may easily happen that circum stances may be occasionally favourable for the passage of slight return shocks through an emulsion ; while on other occasions a thunderstorm may take place in the imme diate neighbourhood of emulsion operations without iu any way influencing the result. The following experi ment will, however, sufficiently demonstrate the necessity of carefully testing plates prepared from an emulsion which has been exposed to the action of electrical disturb ances. A small quantity of gelatine emulsion which was found to yield good results was divided into two equal portions; one of these was placed in a flat glass cell and exposed to the inductive action of a series of elec trical discharges passing between a pair of brass balls two inches apart, and placed immediately outside the glass cell, precautions being of course taken to prevent the light produced during the discharges reaching the emulsion. From each portion of emulsion a plate was prepared, rapidly dried, and exposed, but no difference was noticeable ; the emulsion which had been exposed to the electrical action giving as good a result as the untreated sample. A similar pair of plates, however, which were allowed to dry slowly, showed a result which was in favour of the unelectrified sample ; the plate which was prepared from the electrified emulsion showed that peculiar veil or fog which generally arises from an incipient putrefaction of the gelatine. After both samples of emulsion had been kept for three hours, fresh plates were coated, rapidly dried, and exposed ; but the result indicated that the sample of emulsion which had been exposed to the influence of the electric discharge was undoubtedly in a state of decomposition. Commercial Plates.—There can be very little doubt that the preparation of gelatine plates will become more and more of the nature of a manufacturing operation, and that working photographers will be less and less willing to exercise the constant care and study which are requisite for the production of uniformly excellent dry plates. But, at the same time, every discreet photographer will provide himself with the means of preparing his own plates, and occasionally make a batch, in order to be independent of the plate-maker as far as may be practicable. Commercial plates have now attained a high average of excellence, although it may occasionally happen that carelessness on the part of makers renders their productions entirely useless. As an instance of this we may mention that we recently obtained three dozen plates from a maker of excellent re pute, and on opening the packages were surprised to find that the films were not separated by the usual guards of crimped or kilted paper, but that they were merely wrapped in the orange packing paper, this being in imme diate contact with the films. A very slight adhesion between thepaperand films showed that the plates had been imperfectly desiccated, or that the packing paper had been damp when made use of. Having no other plates at hand, we took them out and exposed twenty-eight of them—but alas! with what result ? Insensitive patches rendered every one useless, the mischief being no doubt due to the contact of the films with the coloured packing paper, the presence of a trace of moisture obviously acting as an aggra vating circumstance. Again, we know of a ease in which, out of a dozen plates, ten were an eighth of an inch longer than the nominal size, and consequently refused to enter the slides ; and we all know what a trouble it is to cut the eighth of an inch from a plate in anearly-dark room. On a recent festive occasion the Rev. F. F. Statham referred to photography as being calculated to indirectly improve the moral and religious condition of the people ; but the dry plate makers had better take care, or some of the expres sive interjections which they may cause photographers to use in the dark room may escape into the outer world, and such an event might cause Mr. Statham to modify bis good opinion regarding photography. A Magic Lantern and Six Slides for Threepence Half- pennij.—A small tin lantern about three inches high, with lamp, slides, and two lenses, is actually being now sold in London at the above-mentioned price ; while a larger one of a similar character costs the somewhat more extravgant sum of sevenpence three-farthings. The small lantern is of German make, and when one considers that the manufacturer cannot get more than twopence for the article, it is a matter of wonder how it can be produced for the price. Very little can be said as regards the artistic merits of the slides, but, like the old Dutch tiles, they at least possess the merit of being hand-painted—if, indeed, this be a merit. The lenses, which as regards optical work are superior to many spectacle glasses sold in London, give, as an advertise ment would put it, “ a brilliant illuminated disc six inches in diameter.” There is also sold in London, at the present time, a toy camera-obscura about the same size as the magic lantern in question. Who knows but what the present pushing age may produce a small tin photographic camera, double slide, two dry plates, and lens for about a shilling ? It could certainly be done if the work were executed on the same scale of cheapness as in the case of the magic lantern. It is, perhaps, not generally known that a very passable photograph can be taken with a common penny magnifying glass, if it be stopped down and a proper adjustment made for the difference existing between the chemical focus and actinic focus. Distortion of Lenses try Pressure or Strain.—Many photo graphers have from time to time remarked that it is occa sionally impossible to focus an object sharply and clearly, even with a lens known to yield a satisfactory result in ordinary cases. Setting aside such obvious causes as light shining into the lens, or the presence of moisture on one of the glasses, there can be little doubt that the most frequent source of the difficulty in question is a bending or distortion of the objective by some mechanical force acting on it. In the case of lenses burnished into their mounts, a
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