CHAPTER II. THE PHOTOGRAPHIC PROCESS.
1. THE STUDIO.
THE arrangement of the reproduction studio is essentially different to that for ordinary portrait work. The general points of such arrangements are described in detail in the handbooks of Drs. Eder and Vogel, and these I may therefore omit so far as nothing novel is to be observed.
We distinguish now between daylight and artificial light studios; further, those in which a camera is used for making the negative and those in which a dark-room itself is the camera. The first will, of course, be used where other things besides reproductions have to be made; the arrangement without a camera presents many advantages for reproduction work only. In the arrangement with artificial light the illumination of the object to be taken is effected as a rule with a source of light which can approximately replace daylight, and which also remains as constant as possible, and the electric light is at present the best. Although other sources of light are sometimes used, the electric light in the form of the arc light for continuous practical use has the advantage. For copying oil paintings daylight is to be preferred under all conditions, and for this the best arrangement is the revolving studio.1
1 See Eder’s “Jahrbuch für Photographie,” 1893, p. 231.
The description of a modern studio with electric light as used in the K.u.K. Militar-geographischen Institut in Vienna, and from which the studio of the K.K. Hof- und Staatsdruckerei was copied, is given here. This studio lies seven metres below the level of the street on the south front of the building, and is shown in Fig. 2.
The preparation and dark rooms are illuminated with white, yellow, and red light by means of two 50-c.p. incandescent electric lamps for each colour, and besides this are provided with window screens of glass of the same colours for daylight.
The windows open into an area 50 cm. wide which runs round the building. The lighting is so arranged here that besides the ordinary collodion plates, very sensitive gelatine plates can be worked. The room C, where the original is placed, is fitted up {31} with four Franzen arc lamps of 3,000 c.p. each for illuminating the original, and the lamps are so arranged that the light falls centrally on the original. The four lamps are fastened by ball
A is the room for the preparation of the plates, for the wet collodion plates, and the silver bath.
B the developing room.
C is the room in which the original is placed, where is found a support for the original TT′, as is shown in Figs. 3 and 4.
D is the dark-room with the focussing table EE′ (Figs. 2 and 3), and is separated from C by a wall of 15 cm. thickness. In this wall is found the photographic lens in a metal flange built into a stout iron box.
F is the washing and polishing room for the glass plates.
and socket arms to an iron frame which rests on rollers; they can be raised or lowered on the frame, and for taking small objects can be pushed closer together. The arms are fastened to the round pillars of the frame, being provided with a screw grip. The lamps can be placed as close as 0·5 m. to the original. As a rule, however, they are worked at a distance of one metre, as then the intensity of the light is about equal to diffused daylight. The axes of the carbons in the lamps are so arranged that the glowing crater formed in the positive pole is turned to the original, by which means the illumination is intensified. The positive carbons have a diameter of 20 mm., the negative carbons 8 mm. The lamps stand in pairs one above the other at LL′. In the two upper lamps the positive carbon is at the top and the negative carbon below it, so that the light is equally distributed over the whole of the subject. With this arrangement of the lamps all reflections are avoided, and neither the grain of rough drawing paper, the relief of an engraving, nor the edges of pieces stuck on are felt. The current is produced by a dynamo in the house; it enters into the place at N, whence it is divided into two circuits of 20 ampères, in which are two switches, an ammeter and a rheostat, and the two lamps on either side.
The wall in which the objective O (Figs. 3 and 4) is placed, as also the brick socle aa and ee (Fig. 2), on which the support for
the original and the focussing screen rest, run on rails, and are absolutely isolated from the brickwork of the building in order to avoid any possible vibrations.
The stand for the original TT′ is provided with screw fittings, cams and wheels, which make it possible to raise the original, to lower it, to move from right to left, and vice-versâ, vertically and horizontally, so as to place its centre axial with the optical axis of the lens, as well as parallel to the focussing screen in the dark room. The whole of the mechanism lies at the back of the stand, so that there is absolutely nothing in front of the original.
The focussing table EE′ is constructed in a similar manner to the stand for the original, and is movable in every direction in the same way. It carries in front two wood clips, in which the board with the original is placed. The table for the original, like the focussing table, is constructed on rollers, which run on the already-mentioned rails. In order to be able to fix these as soon as a sharp focus is obtained a brake is fitted. The placing of the original table at the distance from the lens is accommodated according to the size in which it is to be reproduced, and has already been estimated. There remains, therefore, only to trouble about the fine focussing, which is very quickly effected.
For taking line or wash drawings and for enlargements up to 80 × 80 cm. a Steinheil wide-angle aplanat is used, which gives no distortion. The duration of exposure is with such subjects from eight to ten minutes. For smaller subjects, and principally for photographs on wood, an orthoscope by Voightländer is used, and the exposure varies from four to six minutes.
A Zeiss anastigmat is used for making autotypes. Duration of exposure from three to five minutes. Coloured objects, oil paintings, etc., are taken in the daylight studio. They are printed in the daytime in the open air, and in bad weather or under pressing circumstances in the night by the electric light.