This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
811. When the large camera is used for negative enlarging, it is best to make a contact transparency from the small negative, and then enlarge the transparency. Any size enlarged negative may then be made, limited only by the size of the camera.
812. Having made the transparency, using for example, a 5 x 7 plate, you will next provide an 8 x 10 sheet of ground-glass, or, if you have no ground-glass, flow a sheet of plain glass with ground-glass substitute. When it becomes set and dry, which requires only a few minutes, place the glass in an 8 x 10 printing-frame, fastening it with one tack at each end. In case neither ground-glass nor substitute can be obtained, a very fine quality of tissue paper will answer, pasted over the outside of the printing frame. Place the transparency in a 5 x 7 frame, film side out, holding the transparency in the frame with thumb-tacks.
813. Having secured the negative in the printing-frame, place this small frame inside of the 8 x 10 frame, with the film side out. This will give a space equal to the thickness of the frame between the transparency and the ground-glass (or tissue paper), which is necessary, as with this space, between the two, the ground-glass is thrown out of focus when the transparency is sharp. The ground-glass, or tissue, serves as a diffusing screen and equalizes the light on the transparency. To place the negative too close to the ground-glass, would bring it in focus with the transparency, and give a coarse grain to the enlargement. This is avoided by the thickness of the printing-frame providing a sufficient distance between the two to overcome this grain.
814. Having prepared your two printing-frames, place them in a window with an unobstructed light-a north window preferred. Let the edge of the 8 x 10 frame rest on the window sash, and hold the frames close to the window glass by means of a strong cord stretched across the window, on a line with the upper edge of the smaller printing-frame. The transparency is then ready for enlarging. For negative enlargements not exceeding 8 x 10 inches the Lantern-slide copying board may be used. (See Illustration No. 20.)
Lens To Use In Enlarging. Any lens, other than a single lens, will do. It is preferable not to use a lens larger than the one employed in making the negative; if a larger size is used you will require longer bellows. A smaller size than that employed in making the original negative cannot be used, as it will not cover the plate sharp to the edge; but with, a lens the same size, you can enlarge to any size you desire.
Arranging The Camera. Place the large camera on a table (unless you have a stand for it) and on a level with the transparency to be copied. See that the transparency is perfectly perpendicular, and the camera on an exact line, and level with it. The size of the picture depends upon the distance the lens is from the transparency, also on the distance between the rear of the lens and the ground-glass.
Obtaining The Focus. Place the camera, with the front of the lens within two feet of the transparency, and rack out the bellows until a sharp focus of the image on the ground-glass is secured. If the image is not large enough, push the camera closer to the transparency, and rack out the bellows further, until the correct size registers on the ground-glass. When this is obtained all light between the lens and negative from every side must be excluded. First draw the shades of the window down to the transparency; then extend two wooden strips from the camera to the top of the 8 x 10 printing-frame, and cover this frame with the focusing, or any other black cloth. This will exclude the light sufficiently for the purpose intended, and the principal light will come through the transparency, thus supplying the necessary illumination for the successful copying of the transparency. (See Illustration No. 20.)
Stops To Use. It is always advisable in negative enlarging, to use a stop at least one size smaller than is required to give a good, sharp focus. The stopping accentuates the contrast and gives a more snappy negative. When a transparency is a little flat, having been made from a negative that was a trifle flat, the result can be very much improved by stopping down, thereby accentuating the contrast.
819. On the other hand, with a contrasty transparency, where it is not desired to increase the contrast, use a larger stop. Always focus first without a stop and get as sharp a focus as possible, and then, use what ever stop is necessary to give you the desired result, judging entirely by the appearance of the image upon the ground-glass.