The two negatives, when superimposed for printing, should together have the density of a normal negative, and so the development of the first negative should be considerably cur tailed, while the second one should he developed to the full, under-exposure preventing it from becoming too dense. Practice will soon show the operator the balance to he struck between the two negatives in order to obtain the desired effect.
For printing, the two negatives are placed one on the other in correct register, an operation which presents very little difficulty. It should be understood that the sharp image must be on the outside, so that the two plates occupy the same relative positions as during the exposure. Printing or enlarging is carried out in the same manner as with an ordinary negative, but it is advisable before commencing these operations to bind the two negatives securely together with gummed strips.
Figs. i66 to 168 show the prints taken respectively from the two component negatives and their combination.
313. Production of Soft Focus by Printing. Effects somewhat similar to those produced by the method which has just been described may be obtained by printing from a sharp negative (H. Bouree, 1923). A piece of sensitive paper is fixed in position on a table by means of gummed paper or metal weights. These may also serve as stops for the negative if some other suitable arrangement has not been made, e.g. by driving three tacks into the table at convenient points just beyond the edges of the paper, which in this case should be approximately equal in size to the negative. First, a piece of ground glass is placed with ground surface upwards on the paper, and the negative is then laid on it, gelatine face in contact with the ground glass. A preliminary exposure is given by a matt electric bulb placed about 5 ft. above the table.
Having extinguished the lamp, the ground glass is removed and the negative replaced against the guides in contact with the sensitive surface of the paper. In each case pressure may be applied by means of a thick piece of plate glass, especially if the paper is at all inclined to curl. A second exposure is then given and the paper is then removed and de veloped. According as one or other
of the exposures is made to pre dominate (taking into account the absorption of the light by the ground glass during the first exposure) a soft or a sharp print may be obtained at will. It is easy to determine the " coefficient " of the diffuser used, so as to facilitate any future calcula tions of the partial exposures.
The same working method may be used for enlarging, especially if a vertical enlarger is employed, no registration being then necessary if the paper is properly placed on the projection table.
Mention should be made of another method of obtaining soft-focus prints which consists in interposing between the negative and the paper a thin piece of celluloid or glass during a. fraction of the exposure. If the nega tive is fastened to a mask which ex tends well beyond the edges, and the print is made on a sufficiently large piece of paper, any shift of the paper relative to the negative may be easily avoided when using the ordinary printing frame; the paper is simply held tightly against the mask with two fingers during the opening of the frame and the removal of the trans parent film.
314. Choice of View-point. Although we do not propose, in this book, to discuss the aesthetic questions which arise in the practice of photography, yet we think it necessary to put the reader on his guard against one or two frequent mistakes.
The most favourable view-point for a subject or a group should be chosen without regard to the scale or the final print, but with sole con sideration for the usual rules of composition.
Every photograph should express an idea, conveying to those who contemplate the print the same impression produced at the time the subject was chosen. The picture should contain a principal subject (idea of unity), and should not combine several subjects, each of which presents a special point of interest, with nothing, however, to unite them. The attention should be drawn immediately to the central theme, the eye being led there, not merely by sentirmntal interest, but by the convergence of the principal lines and by the contrasts of light and shade, which should be more striking than elsewhere.