Enlarging Negatives

The negative to be enlarged must be absolutely perfect as regards definition, slightly dense, and full of detail, possessing as little granularity as possible. From the negative, either by contact printing on a dry plate, or copied by the wet process in camera, a transparency should be obtained, the development to be effected by the application of a weak solution of pyrogallic acid, to which a few drops of an acid solution of silver nitrate, 10 gr. to the oz., has been added. The contrasts should not be too decided, nor the shadows too dense. From such transparency the enlargement may be produced by the usual studio process up to six or eight diameters without any visible diminution in the excellency of its definition; or the transparency may be enlarged to the required size at once, and a negative obtained from it on a dry plate as before, or upon carbon tissue, each of which possesses its advantages.

A piece of apparatus for this purpose, which is at once cheaply constructed and easily worked, is shown in Fig. 69.

Fig. 69.

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The chief difficulty in making enlargements, when a suitable camera is not available, is in keeping the support for the film, the lens-carrier, and the negative accurately parallel during the process of focusing the image. For this purpose, the apparatus answers admirably: - A base-board a 6 is taken, having a length of about 2 ft., and a thickness of at least 2 in. In this board a wide groove is cat in the centre, in which runs the thinner slab c, which carries the upright support d. Two narrower grooves are then made on each side of the centre groove, in which run the two square rods e, which carry the rectangular support/. A glance at Fig. 69, will show that, when closed, the lens-carrier d, and the support f, are about 2 ft. apart, but that they can be separated, while still keeping parallel, to nearly three times this distance. The size of the board / and indeed of the whole apparatus depends upon the size of the enlargement required; but it should, of course, be made to suit the largest size that could possibly be wanted. It is important, also, that the board should be made of sufficiently stout material to prevent any danger of warping.

The front d is also grooved so as to take the ordinary sliding front of any camera, so that the lens may be raised or lowered as required.

The remainder of the process is very similar to that adopted with an ordinary enlarging camera. A hole is cut in the shutter of the window of a dark room,and a frame made to take the negative. It is important that the plane of the negative should be parallel with the plane of the shutter. The above-described apparatus is then placed in position before the negative, and a hood of black cloth is arranged so that all the light which passes through the negative can pass only through the lens. There are many ways of contriving this, such as simply nailing one end of the hood to the shutter around the hole, and securing the other end with a rubber band around the lens, taking care to make the hood large enough to keep clear of the negative. Having once got the baseboard of the enlarging apparatus accurately adjusted to the plane of the negative, it may be securely clamped in position, and all further adjustments made by drawing out the lens carrier and the support /, to any required length. Focusing can be perfectly well done by this means; but it is, of course, better to finish the focusing by means of a screw, if great accuracy is required.

The support /, if used for enlargements on paper only, is sufficient without any further arrangements, as the paper can be secured in position by pins. Opals, also, can readily be secured by small nails or drawing-pins. For developing dishes, the cheapest substitute is stout tin, well covered with black enamel, which can easily be renewed when necessary. When enlarging by daylight, fasten a piece of thin tissue-paper behind the negative, and reflect the light upon this by means of a plane mirror, fixed at a suitable angle. By the diffusion of the light by the tissue paper, great uniformity is ensured. The whole apparatus, as above described, can be made by a good carpenter for about 10-12s. - (J. Vincent Elsden.)

Following is an economical method of converting the ordinary view camera into an efficient projecting lantern without in any way impairing its usefulness in its more legitimate field of operations. With a suitable lens, it will do the work of the vastly more expensive apparatus devised for the special purpose of projecting enlarged images. The accompanying roughly drawn sketch (Fig. 70) will, in connection with the description, make its construction sufficiently evident to enable the tinsmith to duplicate the apparatus.

Fig. 70.

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Referring to Fig. 70, a is the camera proper; b, c, d, c, and f are the attachments devised to convert a into a projecting lantern. The form of camera best adapted for this use is one of front focus, having a square and removable reversing frame and a moderately long bellows. A little ingenuity, however, will easily find a means of making the changes necessary to adapt the attachments to other types of cameras. 6 is a wooden box, having the same outside dimensions as the reversing frame, whose place it supplies; it is fitted accurately to the camera back, to which it is fastened in the same manner as the reversing frame. It is, of course, open in front, while to its back is fastened by a flange the circular sheet-iron collar c, in which the condensers are inserted. d is a sheet-iron cylinder attached to the lamp cover e, as shown. In the figure it is represented as detached from c, over which it slides when the apparatus is in use. / is the lamp, the double or triple wick one in common use in the oil lantern. It may be round or square, and it is covered by the cylindrical body e, which is surmounted by a chimney. If preferred, this body can be made large enough to fit over the lamp instead of surmounting it as in the cut.