MODIFICATIONS OF THE CARRIER, ETC.
The carrier holding the negative may be made to raise and lower, or move from side to side, in order to obtain a more posing the reflector does not receive an unobstructed view of the sky, it will yet give the field even illumination. More over, the opal can be kept cleaner than the painted board. The camera may be of the simplest form, in fact the simpler the better. In some cases it even eon central image ; or in cases where only a portion of the image is to be enlarged. Such an arrangement is shown in Fig. 427. The reflector may consist of a sheet of polished tin reflecting the sky, but it is preferable to use a board painted white or a sheet of opal stoutly framed ; the advantage of the opal being that, sup silts simply of an arrangement of rods be tween two frames, over which a cloth is thrown, as shown in Fig. •2S. Such an arrangement is easily made, and the ex pense of a large bellows obviated. This point is of little consequence except in large cameras. With reference to the
lens, any good quality lens is suitable, and, generally speaking, one of large aperture is to be preferred. Flatness of field is an essential qualification, for an image on a flat surface has to be trans ferred to another flat surface. It is im portant that the camera should focus either by movement of the front part or running on the wall, which are gripped by clips attached to a board as shown in Fig. 420. advantage of such an by rack and pinion adjustment on the front lens. All cameras which have their adjustment in the back frame are unsuit able, as in focussing the light is let in between the frame and the carrier. Most field cameras are nowadays made on the former principle, but these are not always solid enough for commercial enlarging.
apparatus is that the guiding rails are out of the way, and there is no fear of