SearchAbout This SiteTreatment ForumVideo clipsGalleryScienceLibraryTechnology

Towler, John. The Silver Sunbeam. Joseph H. Ladd, New York: 1864. Electronic edition prepared from facsimile edition of Morgan and Morgan, Inc., Hastings-on-Hudson, New York. Second printing, Feb. 1974. ISBN 871000-005-9

Chapter XXVII.
COLLODION NEGATIVES OR POSITIVES COPIED FROM COLLODION OR PAPER POSITIVES.

IN this chapter will be described the method of copying photographic or typographic prints. Three things are absolutely requisite in order to secure a good copy; these are, as before, a good lens, good light, sharp focussing.

For the purpose of copying I invariably use the full blaze of the sun. Some artists pretend that the system is false. They take their ideas from the effects produced on solid objects, where the contrasts are so immensely exaggerated; and they do not bear in mind that on a flat surface there can be no shadows, because there are no prominences. All the contrast that can possibly be obtained in the copy, exists already in the original.

Upon a light built table or board, two inches wider than the camera, nail down on either side a ledge of wood, within which the camera can slide longitudinally. At one foot's distance from one end erect a piece of board of the same width as the long board, and a foot high; let it be fixed perpendicular to the board and to the direction of the ledges, by means of triangular braces near the end of the long board. On the side fronting the camera, construct two beveled ledges, one on either side, perpendicular to the base-board, of half-inch material; within this a piece of half inch board, six inches wide, is correctly adjusted by planing, so as to slide up and down with facility; on its surface on either side is a similar bevelled ledge running horizontally, in which another thin piece is made to slide with ease. This last piece is the holder of the print to be copied. By the construction it will be seen that the holder admits of motion vertically and horizontally, and that thus the print can be accurately adjusted in a correct position in front of the lens, so that the center of the print and the axis of the lens coincide. The print, too, will thus be parallel with the ground glass in the camera. Small slips of tin plate are screwed on the surface of the holder, in order to clamp down the print, and to prevent any unevenness on its surface by cockling from the heat. Pins or tacks are inadmissible here, because of the shadows produced by them on the print to be copied. As soon as this mechanical contrivance is complete, slide the camera up to the holder, and adjust the latter so as to bring its center in front of the cap of the lens, and with a pencil draw a circle around the cap and upon the surface of the holder. Whilst the slides are in this position, mark the vertical and the horizontal slide, so that at any time afterward the holder can be brought into position with great facility. The holder is now taken out, and the print to be copied is fixed, so that its center coincides as near as can be with the center of the circle; it is placed upside down, so that its four boundaries are vertical and horizontal. Now slide the print-holder into its place, and slide back the camera until the. picture on the ground glass is of an exactly equal size with the original. A microscope is required in this operation, in order to focus with the utmost accuracy. Do not despise the microscope, it is almost indispensable. Focus whilst the sun is shining upon the picture. Use a very small stop. Let the sun shine from one side slightly, with your back turned toward this orb. The most agreeable time to copy by this method is early in the morning; the light is then clear, and by turning the table on one side, the rays illumine the object very brilliantly, and without any haze; turn the table always so that no shadow of the camera or lens falls upon the object. As long as the sun shines, you can thus copy, and copy perfectly; the morning hours being personally more agreeable, photographically perhaps not as effective as toward noon. The time of exposure will vary according to the power of the lens, the size of the diaphragm, and the magnitude of the copy. With a lens of three inches focus, of C.C. Harrison's manufacture, with a diaphragmatic aperture of one third of an inch, and when the copy is equal to the original, an exposure of fifteen seconds will produce a rich negative. The same conditions remaining, the one fourth orthoscopic lens of Voightlaender, whose focus is about twelve inches, will require an exposure of between two and three minutes to produce the same effect.

By the first-named lens, an ambrotype or melainotype will require only two or three seconds.

By adhering cautiously to the rules prescribed, and above all things by very accurate focussing, and by taking care that the surface of the photograph, plate, or print is perfectly smooth, and in a plane parallel with the ground glass, copies can be obtained that can scarcely be distinguished from the originals. But a very slight undulation on the surface of the print, or deviation from parallelism is sensibly observable when the conjugate foci are equal, and much more so when the copy is amplified. The camera, when once adjusted for the day, is strapped down firmly to the board, so that the conditions of focussing can not be altered by inserting the tablet, etc. It is necessary to cover the whole camera, and especially the posterior opening, with a dark cloth, lest a single ray might penetrate into the interior. Close the lens always with the cap before you take out or put in the slide, because it is easier to move the cap than the slide. After the slide has been taken out, wait until all oscillation or vibration has ceased, before you remove the cap. Perform all your motions in this operation firmly, but with gentleness, not roughly and in haste. Whilst the ground glass is out, place it where no reflection can interfere with the print to be copied. The board on which the camera slides, as also all the other parts, had better be stained black, or of some neutral tint.

If the light of the sun could be directed through a long cylindrical opening, and then applied directly to the illumination of the print, without interference from reflections in all directions, the operation would be neater and more effectual.

Where copying has to be performed by diffused light, this light must be small in quantity, proceeding from a single pane of glass, as reflected from a white cloud or a white sheet, and all reflections must be carefully avoided. The management of the light in copying is reduced to very simple conditions-a single light is all that is required-no more contrast is required; see that none is communicated by unnecessary and extraneous shadows from neighboring bodies, caused by secondary light. A single light, where there are no bodies in its direction to the print, will produce no shadow, consequently all shadows must proceed from secondary lights; shut up, therefore, every aperture, excepting the one which is to illumine the print or type to be copied. These precautions will bring with them success; the neglect of them will cause you to quit copying with disgust for want of success.

With such a contracted light, the illumination can not by any means approach that produced by the direct rays of the sun; the consequence will be firstly the necessity of using a large diaphragm, and of thus diminishing the sharpness of the copy; and, secondly, of increasing the length of the exposure. The difference of illumination in copying and in direct portraiture is very distinct; for the latter purpose a single light without reflection will not, can not succeed; whereas for copying, more lights than one would be not only so much more than sufficient, but at the same time probably in most cases injurious. Do not, therefore, confound the two operations, and blame the light for your mismanagement of it, for in nine cases out of ten your want of success is to be attributed to this mismanagement.


Home ~ Library ~ Science ~ Technology ~ Gallery ~ Video ~ Forum ~ About ~ Search