Volltext Seite (XML)
112 THE PHOTOGRAPHIC NEWS. [MARCI 7, 1862. With respect to the diaphragm that I recommend so strongly for the studio camera, to he placed in front of the plate, at a distance of about an inch and a half from it, this protection is still more necessary in the field camera. While a landscape picture is being taken there is a greater amount of white light inside the camera than when a por trait is being taken in the studio. In the latter instance the aperture used is generally larger, but the principal ob jects covered by the lens are of a sombre hue ; in landscape photography the lens is more stopped down, but about a third of its range mostly includes a bright sky which throws a great volume of white light into the camera. Several cameras from their form do not admit of such a diaphragm being introduced, as it would interfere with some of their parts. I think that these should only be used for exceptional purposes, and cameras whose construction and design permit ot this protection being added should be pre ferred for general use in the field. In most instruments a diaphragm of this nature may be employed, the frame of which exceeds slightly in breadth that of the frame of the plate holder ; (see fig. 8, showing a sectional plan). This will be a great protection to the plate, but it would be still better if this diaphragm stood out an inch or an inch and a half from the body of the camera. This could only be effected by making the camera or at least that part of it slightly larger in all directions ; and the photographer must decide whether he considers the advantage to be gained by doing so is equivalent to the trifling extra bulk. Fig. 8. camera is “ cocked," and a set screw serves to clamp it in position. As the cases in which the camera requires to be tilted are not of very frequent occurrence this is not a necessary addi tion to all cameras, but as I have before remarked cameras that are not provided with it must always be placed hori zontally to obtain an exact representation of any subject. The camera is generally attached to the tripod stand by means of a large headed bronze screw passing downward through a hole in the. bottom of the camera body, and clamped underneath the triangle by means of a nut. It will be found advisable in all cameras to reverse these parts, and to fix the nut a (fig 9) permanently on the inside of the bottom of the camera body 6, the flanged screw d, passing through the boss of the triangle c, as usual, works into this nut and clamps the body and triangle together. The ad vantage of this plan over the uusal loose nut and screw arrangement is that it is more easy to use, and the camera Fig. 9. When an object has to be photographed that is cither wholly or in part above or below the range of the lens when the camera is in a horizontal position, so that the instru ment has to be “ cocked ” upwards or downwards to bring the picture into the proper place on the ground-glass, it is necessary to have a camera with a swing back, to avoid the image being distorted, which it will always be when the plane of the object, and of the plate upon which its repre sentation is impressed are not parallel to each other. In representing horizontal lines on different planes this effect produces perspective, and is necessary to the proper delinea tion of the picture, but all the vertical lines of every view being in reality on parallel planes, must also be represented truthfully parallel to each. A swing-back is rather an expensive addition to a camera, and, therefore, very few are supplied with it; but whenever the camera has to be “ cocked ” it is absolutely essential for architectural subjects in which the slightest distortion is so immediately visible and unsightly, and, indeed, without it the truthfulness of the copy is impaired in every subject, although the fact may not be so readily detected in ordinary landscapes without buildings in the first or second plan. A swing-back consists of a frame into which the plate slide fits and which is swung at the middle upon two pivots one on either side of the camera. Accuracy of fit is gene rally depended upon to secure the exclusion of all light at the joints, but it would be safer, I think, to place a bead inginside to intercept any stray ray that might filter through, in the same manner that I have described for the studio camera body. A rack and pinion are generally added, by means of which this back carrying the foccussing-screen or plate-slide is brought parallel to the horizon when the if a folding one, or one that has to be prepared in any way before it is ready for use, can be attached at once to the stand, before opening it, and it is thus in a more conve nient position to complete the necessary arrangements. Also it reduces by one the number of small loose objects which have to be taken into the field, that run the chance of being lost or left behind, and whose absence is always» source of annoyance, even if it does not bring the day’s wor- to an abrupt end. {To be continued.) INSTANTANEOUS PHOTOGRAPHY ON ORDINARY TANNIN PLATES. BY HENRY DRAPER, M.D., OF NEW YORK. The process consists essentially in keeping the plate at s high temperature during development, the developer itself being poured on when at the ordinary temperature of th® room. I obtained a street view with a lens of 1]-inches aperture, in less than a second, the plate during develop- ment being maintained at 200° F. In a communication to the American Photographic Society at its last meeting (February 10th, 1862), the details of the process were given, and are published in the Americt^ Journal of Photography. They may be briefly recapitulated as follows :— • A plate is prepared in the manner recommended by Majs' Russell, except that the film is held at the edges in the wa! commonly in use in American, that is, by a rim of a solutiob of albumen one part to water six parts. After exposure in th. camera the plate is heated in hot water. The ordinary develop 1 ’' not having been warmed, is poured on as soon as it comes o“ of the water, and worked in the usual manner. If the plat, cools sensibly before the picture is developed enough, hot wate is to be poured on, and the development then continued. At a trial before two of the best amateurs of our Sociel! Messrs. Hull and Cottenes, in my father’s (Professor J- ' Draper) laboratory, in the University, by using water on X at 130° F., we shortened the exposure to one-twentieth that which was necessary when another of the same set u plates with the same diaphragm was used, and developed f I the ordinary way with water from a tap. The length I Mar tims rei into wl shorter been us tried it photog apertur the gre methoc used h as in t cold. Pro streng ad van Uni Th Hyc sulpha import chemic the ga the ve with n three c tative form i passed are not hydro; down I by am tated 1 line s< silver, mercu cobalt the th necessi the ar the hr be red i whilst colour the fir the otl bodies enabl of a r cadmi will s mospl of a n yello oxide sulph of tl yello but ( drog The is al sulp is v whit on t cipa grap phui wher silver