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.
Enlarging. When making quite large copies from small originals, sometimes the lens employed is of too long a focus and the bellows in the camera will not admit of enlarging to the largest size plate your camera will receive. You can then lengthen the camera by adding a cone extension to it. The cone can be made of light wood, box-shaped, open at both ends, and made of a size to fit one end in the front of the camera in place of the front-board, the lens being attached to the other end. (See Illustration No. 2.) This box or cone should be made about 14 inches in length, and must be painted a dead black color on the inside, to prevent any white reflection, which would fog the plate.
Illustration No. 3 - See Paragraph No. 489 Colored Daguerreotype Copied with Ordinary Plate.
Illustration No 4 - See Paragraph No. 489 Colored Daguerreotype Copied with Orthochromatic Plate.
Stops To Use. There is no set rule to follow regarding the necessary stop to use. One must be guided entirely by the appearance of the image on the ground-glass. Always focus with an open lens and then gradually stop down until the image appears as sharp as the original to be copied; then use the next smaller stop and you will have plenty of sharpness, and by giving full time you will preserve all the quality there is in the original. Remember, when enlarging, the more you enlarge the smaller the stop you must use in order to retain sharpness and roundness, and, of course, you must time accordingly.
Fogging The Plate When Copying. Pictures which are mounted on white card-mounts, with a wide margin surrounding the print, will fog the plate, especially if a long exposure is required. The white card margin will reflect the light into the lens, and this reflected light acts more sensitively on the plate than the light reflected from the original picture to be copied. Consequently, a long exposed plate receives more reflected white light from the white margin than it does from the picture. To avoid this reflection make a mask of some dull black paper; cut out an opening the size of the picture to be copied and cover the cardboard entirely with this black mask. You thereby avoid any further reflection.