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July 24, 1863.] THE PHOTOGRAPHIC NEWS. 357 in the other products of art, bear the stamp of his indi- but, as to what a lens will cover, I am thoroughly convinced ’ IT ° ' . r , , while the triple worked much closer to the outer line, and pon this communication the president, M. Kegnau , then finished off more abruptly, or with a sharper edge. marled +hat 110 —• ± at Blaneuazt Evgaxd's re- n r‘. ... . . 1 nr % . .— : 1 r lens, 7 in. locus, mcruamg an angle oi neany I , an M: 1 oitevin, who presented the Society with some proots the base line of the picture only measured 81 inches. +ainnc NMA. An..1 Lx. ovnregseS hmselt on 1 . .I . *. quired angle, but whether it would work satisfactorily in other Should I be in error, doubtless you will put me right. TAXXO-GLXCERIXE. to vases as a decoration, but he, at the same time, seeks the obtained upon enamel by vitrification, expresses himself on ■ this subject in the following terms:— “ I do not for a moment wish to enter upon any discussion on the various processes which have been and arc now em ployed by other photographers to produce photographic impressions by means of vitrifiable culvers upon glass, porce lain, or enamel; although very probably the insolubilizing, of light upon bichromatized organic matter is the basis of these various methods, bitumen of Judea having, I believe, been abandoned for some time past by the skilful operator, who extolled its use in 1854. You know, also, that previous to 1855 no one had employed the bichromates with organic matters to produce permanent pictures on paper or other surfaces, before the announcement I made at this period. “ The vitrified proofs upon enamel which 1 submit to the appreciation of the Society, have been obtained by my pro cess on glass, prepared with per-chloride of iron and tartaric acid, which, since 1860,1 employed in carbon printing. In the present instance 1 employ instead of carbon an enamel in impalpable powder to develop the picture. 1 .. this latter, by means of a film of collodion, on to a plate of enamelled copper, or porcelain, &c., and 1 fix it by means of a sufficient heat, in an enameller's muffle.” Of course, the image formed with the 11} in. focus lens, was larger than the other, and, consequently, the angle of view, the muffle only a dead, light rose colour, but by modifying this first attempt M. Bey rich hopes soon to succeed in con verting this proof into vitrified pictures. WHAT A LENS WILL COVER—ANGLE OF VIEW —EQUIVALENT FOCUS. 1 in. or 11 in., more. This brings me to the next nearest advertised lens, the aplanatic of 12 in. focus. Now, cither of I transfer I length, we then should not be bothered with such remarks as nominal ami real focus, which are very perplexing. Now if the back focus is 10 in., the real focus will probably be viduality." There is, therefore, unless I deceive myself, a new road open to photography : I should add, that apart from this point of artistic view, which is the most important part of my study, there is another purely photographic, to which I ask permission to call the attention of the Society. We know that photography is condemned to produce in one and the same unit of time, a combination of objects pos sessing extremely diverse photogenic properties. Hence arise the disparities of hue and the false effects we frequently encounter, even in the most magnificent proofs; and if in ] certain pictures the waves of the sea resemble black ink, and the guides upon Mont Blanc resemble chimney-sweeps, it is because it is impossible for the most skilful operators to make the objects appear with their local tones in the same space of time as luminous clouds, glaciers, or snow. This example among a thousand will suffice to make us appre ciate the advantage which may be derived from the possi bility of completing, by a subsequent exposure, those parts of the image where the action of the light has been insuffi cient during the exposure in the camera, or by the attenua tion, by purely chemical means, of the lights too vividly marked during the first exposure upon the parts too strongly lighted. (apart from the evidence published in a contemporary, re specting a picture of Whippingham Church, by Mr. Ernest Edwards), that the triplet form does cover a very wide field. I made the experiment a few days since of taking a view 11 by 9, with the No. 1 triple of 7 inches back focus, and another the same size from the same point, with a caloscopie of 11} in. back focus. The triple gave a larger circle of light, and better defined to the edges than the caloscopie : the latter seemed to soften down the outer edge of the circle, like a vignette, a much greater distance into the field. remarked, that the assistance M. Blanquart Evrard's re searches could render to photographers consisted in the larger tr power it gave them of modifying at will the effects of a given I smaller, negative. To turn it to useful account, it would be desirable to make two negatives, so that one might be submitted unhesitatingly to every kind of experiment, and that if damaged, there would remain the other to fall back upon.. I next turned my attention to some pictures sent me by a friend who swears by the “ aplanatic ” form, they were very good but accompanied with a note “ taken with the aplanatic lens, 9 in. focus, including an angle of nearly 70°," although the base line of the picture only measured 84 inches. This is an error committed, I am afraid, too frequently, in stating the angle included by various lenses ; it is a subject that I much wish some of your numerous contributors would take up, and treat in a popular manner with diagrams, &c., for, according to my calculation, the pictures in question would only include an angle of a trifle less than 50°. This is, per haps, as much as most photographers care for, and certainly is a wonderful improvement on the old form, which only includes about 38°; yet in stating the angle comprised in a given picture, and by a certain lens, it ought to be done correctly, or others are likely to be misled by it. I am going on the supposition that in speaking of the angle of view it is measured on the horizontal or base line of the picture, and not diagonally. I find that to include an angle of 60° on a plate 11 by 9,1 shall require a lens of about 96 in. focus. Now, in searching the lists of our best makers, I find no such focus quoted: there is a triple of 10 in. back focus. I wish all could be induced to state the true focal Sib,—Being in search of a good landscape lens to use in a camera for 11 by 9 pictures, for general purposes, and also for engineering subjects, bridges, &c., where a large angle of view is required, say 60° or 65°, I ask the favour of your advice as to the form of lens best adapted for such purpose. It is not a question of maker, as I am satisfied there is little to choose between three or four of our best manufacturers ; means of baking these pictures, so as to convert them into [We do not know of any lens at present catalogued which vitrified proofs. Success has not yet crowned his efforts ; the I will give you an angle of 60° or 65° on 11 by 9 plates, gold deposited upon the silver during the toning, yields in The only form of lens which will give the required angle M. Beyrich, of Berlin, presented to the Society some vases , . , of glass porcelain, &c., of various forms, to which he has these for a picture, 11 by 2, will not include in rpund numbers found the means of applying ordinary photographic proofs, more.than.5001 there is, then nothing left to fall back upon His process is based upon the discovery he has made of a I but the aplanatic of 9 in. focal length i, tins would give the re- paper from which the sensitive coating is easily detached; ■ * , . . J — ths paper, treated in the ordinary manner, resists until after respects 1am wishful to know, and also if at the same time it has passed through the toning baths; it is then only that lyou could.inform me th 0 focus o the No. 2 it becomes easy to separate the printed picture from it as a , triple of 10. inches back focus. W bile writing the foregoing sort of film which may be glued upon glass or porcelain have received the Notes for the loth inst., in which Mr. vessels, whatever betheir form. This application made to 1 Sutton .speaks favourably ot a triple lens of 14'6 focus for small ground glasses constitutes images visible by trans- I I bY 10 pictures ; now this, according to my previous mode sparency analogous to lithophanes. Hitherto, M. Beyrich | of calculation, only gives an angle of 45°. hmllki has only succeeded in transporting the picture in this manner "" "" " "" " " ' *
