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The photographic news
- Bandzählung
- 6.1862
- Erscheinungsdatum
- 1862
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- Englisch
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- F 135
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- http://digital.slub-dresden.de/id1780948042-18620000
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- Bandzählung
- No. 188, April 11, 1862
- Digitalisat
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Zeitschrift
The photographic news
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Band
Band 6.1862
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- Ausgabe Ausgabe 73
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- Register Index 619
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Band
Band 6.1862
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176 THE PHOTOGRAPHIC NEWS. [April 11,1862. APRIL such circumstances I should use the bromide considerably in excess of the iodides. The nitrate bath should be of the strength of 40 grains, satu rated with iodide of potassium, and perfectly neutral. I need scarcely remark that the utmost care is necessary in the preparation of the bath, also in the selection of nitrate of silver, which should be pure recrystallized, otherwise the amount of acid to prevent the plate fogging will materially injure the sensitiveness. We do not experience this so much in ordinary working, where the time of exposing the plate is not limited. With every caution in preserving the bath from injury, I have never been able, in working instantaneously, to use it more than five or six days ; after that its sensitizing pro perties diminish rapidly, but it is still very good for general purposes. Another important point, too, is to expose the plate within a very short time after its removal from the nitrate bath, or it will lose much of its sensitiveness. Here is one great cause of its failure, as oftentimes the sun disappears behind a cloud just as the plate is no ready. There is no remedy but to try again. A word or two may here be said upon the form of lens best adapted for rapid working. For street views and public build ings, I find it a great advantage to bo provided with three sets of double achromatic of the respective focal lengths of 5}, 4}, and 8} inches. By this means one is enabled to enlarge or reduce the image to the size suited to the plate. I prefer using the first-named, being with that enabled to use a larger stop; but in copying architectural subjects in crowded localities, want of space oftentimes compels one to resort to a lens of shorter focus, and consequently a smaller stop. In all cases it may not be convenient to be so liberally provided. To those not having at command a variety, I would recommend a lens of 4}-inch focus as being the one most useful. Cannot some of our best opticians construct for us a lens which would enable us to vary the size of our picture where distance, or rather the want of distance, confines us to one spot ? What, for instance, displays worse taste than copying a public build ing, leaving out foreground and sky? and yet the operator is sometimes reduced to this or leave out altogether. I have made many experiments in the mode of exposing the plate, in placing the shutter in front of the lens; also imme diately behind it; and lastly, near to the plate, which answers perfectly. I have found, by using the drop in front of the lens, a want of definition in the corners of tho negatives. I men tioned this fact some time since to my friend Mr. Dallmeyer, and should be pleased to hear if he has devoted any attention to the subject. By placing the shutter on the dark slide, and having a contrivance to lessen the size of the slot, we can get different lengths of exposure, which is sometimes an advantage, although, of course, it is advisable in all cases to give the shortest amount of exposure the sensitiveness of the plate will allow, otherwise moving objects will not be well defined. The developer I generally use is proto-sulphate of iron, 2 oz.; water 1 pint; acetic acid, the least possible amount, which I determine according to the temperature, varying from 4 to 8 drachms. Should too much be added, it is not so easy to develop objects in the shade. After the impression is fully developed, strengthen with pyrogallic acid. I have now, gentlemen, given you the details of my mode of operating, and shouldl noteave made myself sufficiently under stood, I shall be happy to nswer any question. In conclusion, I beg to thank you for your patient attention, and to assure you that I shall be pleased if what I have said should elicit further information from the members present. PHOTOGRAPHIC MICROGRAPHY. BY A. 1. NEYT.* The study, so full of attraction and mystery, of the infi nitely minute in creation, by the microscope, has induced me to seek some practical method as a substitute for draw ing,s designed by the hand, or by the aid of the camera lucida, a mode of reproduction at the same time more rapid and more exact. Until the present time, micrographists are constrained to design their own drawings, and, if they wish to publish, entrust- to engravers who are strangers to the science, the retracing of these designs. In this way impor- * Bulletin Beige de la Photographic horizontally ; we are obliged, therefore, to work on I on lese rays leave the instrument, when I use THE • The Sa seldom. outburs :it a grauuaicu 2—,. at the point where J it horizontally or in vertical plane, which is very troublesome when operatin’ liquids, which is necessary in the reproduction of dark char throw th camera w ■mins t which it c obtained, the image screen or behind, a however, of the len over the possessing operation glass, in View, the S*. V eamera I glass, tak light. I that ever length of It good i times ma Those of of a seco: shutter, : by a litt striking i The pr purpose i operation known r &oria a ; rapid me increased ■nay be,: these cili and defo view I hi urrent. battery, i poles sha is intern hear my the glass the posit from the interposition of two prisms is nearly nil. . 8 Directly under the object is placed a graduated series-. diaphragms. I have added to thi fusaria. | The little glass which covers the object is retained, it % true, by the drop of water; but, if it Be a little too heav); the whole of it glides insensiBly from its position, an delays the work. If this do not happen, another obstac’ I presents itself: the water has a tendency to form near t edges of the thin covering glass a greater depth than at t centre. The animalcules seek refuge incessantly in tb greater depth of water, finding here greater liberty, a they are, consequently, always going out of the field of th apparatus. To obviate this inconvenience, I have broug" the plate of the instrument into a horizontal positio interposing under the focus an illuminating prism, aa then immediately above the object-glass a second prism (tl is of quartz, and as small as possible), which sends the ra I in a horizontal direction. In this way the difficulties SI tailed above may be removed, and, for the rest, all reman in the same condition as before. The loss of light arisl ’ contact, in the p OPeratioi , When brovnc Avail my dtce uni Wanner photoges The a microsco great sei plying t Rcopic i Of a ver impressi ingeniot possess i hand of at a pri that of t tant details are often neglected or falsified ; for it is very difficult to an artist, and even to some scientific observers, to avoid following their own views or fancy in rendering those parts which the microscope has not perfectly resolved. It thus happens that new discoveries often give rise to discus sions, and, as it is at times difficult to preserve an object more than a few hours, it becomes impossible to submit it to other observers, in order to decide the matter mor# positively. I have thought .that photography could remove these obstacles, by furnishing a means, rapid and faithful, of reproducing the observations made by the microscope. At the period when I commenced my researches, I was ignorant of the fact that M. Bertsch, of Paris, who has rendered much service to science, had already produced several photographic proofs of microscopic objects. An English photographer, and also another in Munich, have been equally engaged in these experiments; but no one has up to the present moment reproduced living ani malcules, such as infusoria, and it is upon this branch of the science that I have directed my efforts. I send you herewith some examples of my labours. The apparatus of which I have made use is the helio graphic microscope of M. Bertsch, constructed by M. Hart nack, a worthy successor of the celebrated Oberhaeuser, his uncle. This instrument is very perfect, as well in it mechanical as its optical arrangements. The general appearance is similar to an ordinary solat microscope. The mirror with parallatic movement, serving to reflect the solar rays in a constant direction, is replaced by a large prism, which gives a complete reflection, and offers less resistance to the wind. The stability is thus very great. The achromatic condensing lens is 22 inch in diameter. The focus is provided with three converging lenses, which may be used cither alone or simultaneously- according to the power of the object-glasses employed. I have attached to this, two diverging lenses, completorf to the focus of the condensing lens, in order to obtain * beam of parallel light in cases where I use lenses of larg‘ field, such as are necessary to obtain great sharpness. Tb? apparatus is achromatised in such a way as to make the fod yellow and violet rays correspond, these latter being th’ actinic rays. In ordinary apparatus, as is known, it is th' yellow and red rays which are united; but in this case, W* much heat would be developed on the object to be repfl duced ; besides which, we should have a visual focus whid would not coincide with the chemical focus, and this would give rise to an almost insurmountable difficulty in focussing an operation already more than sufficiently delicate. Tb‘ microscope constructed by Hartnack transmits all the ray
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