ENLARGED NEGATIVES.
These may be Made with the apparatus already described, by placing suitable rails across the easel to carry the plate as shown in Fig. 4-16 ; the method of procedure in all other respects being pre cisely similar. Of course, the exposure, being upon a plate instead of a paper, will be proportionatel:, less, and the negative from any picture, the picture is pinned on a board and fixed square and parallel with the camera ; the camera is considerably extended, according to the size of the image required and the focal length of the lens. The bellows must open out to at least twice the focus of the lens. A small stop and slow plates should be used, and when the original is weak in contrast a. hydroquinone de veloper is suitable. The shorter the focus of the lens the less extension of camera is required. The amount of enlargement is governed by the sharpness of the original photograph and the texture of the paper of the original and of the required print.
About three or four diameters is the usual enlargement ; beyond this the grain of the paper becomes so apparent as to kill delicate shades of the picture. However, the coarse grain can be almost entirely obviated by copying in sunlight or under glass, yellowness by using isochro nettle plates. With glass the difficulty is to avoid reflection, and no rule can be laid down, so much depending on sur roundings. It is generally best to have a strong front light and the sides screened in the manner presently to be described, whilst any bright metal work on the front of the camera should be covered. To get a print under glass, that is, in optical contact with the glass, immerse the two in water, and float the Knit on to the glass under the surface of the water. Copying is best done by daylight, but it may be successfully clone also by electric, magnesium, gas, or lamp light, but in the