Page:Graphic methods for presenting facts (1914).djvu/350

 used for a reduction through quite a range of different sizes by holding the glass at different distances from the drawing which is being considered.

One of the commonest errors made by the beginner in preparing charts from which printing plates are to be made is that he does not allow for the reduction in widths of the various lines. If the printing plate is to be made one-third the lineal dimension of the original drawing, it is essential that the lines on the original drawing should be made three times as wide as they are to appear when printed. The novice will find that even though he uses a reducing glass with great care, his heavy lines will at first nearly always appear less wide and black than he had expected and hoped that they would be.

Quite often it is desired to change the proportions of some chart so that the ratio between height and width may be different from that of the original drawing. Though the photographic process used in the photostat machine or by the engraver (in making plates for printing) permits a change in size, the same proportions remain between width and height. There would seem to be enough demand to justify an engraver making a combination of lenses by which one dimension of a drawing may be changed more than the other dimension. By using two lenses having cylindrical surfaces and having the axes at right angles, there might be a possibility of changing the proportions of drawings which are copied without any great amount of expense after the apparatus has once been designed.

Very often persons owning cameras do not know that the camera manufacturers are in many cases able to supply auxiliary lenses by which pictures and copies of drawings may be made practically full-*size with ordinary cameras. Though the arrangement is not as convenient to use as a regular copying camera, it may be of great service to supplement the work of a camera already owned.

It is not generally known that line plates may be made from charts drawn on co-ordinate paper ruled with green ink. Such charts sent to many zinc engravers are returned with the statement that it is impossible to make a line cut from green-ink copy. The statement is made in most cases by the engraver without even attempting to make the cut. There is no difficulty in making excellent zinc cuts from copy using the ordinary green ink, and many of the cuts in this book have been so made, as, for instance, Fig. 156, Fig. 207, and Fig. 215.