VISION AND THE TECHNIQUE OF ART. 



27 



which means that a series of points subtending equal angles in space 

 are not imaged at equal distances on the retina. The images of equi- 

 distant points at a distance from the axis are closer together than those 

 near the axis, the farther from the axis the closer they are together. 



Figure 33 shows the approximate distortion which exists in the eye. 

 If the eye looks at the center of a rectilinear grid, similar to the one in 

 the figure, held at such a distance that when looking at its center the 

 corner will subtend an angle of thirty-two degrees with the visual axis, 

 the picture that is formed on the retina will not be a reproduction of 



Figure 33. Curves showing the "barrel" distortion of a rectilinear grid 

 that takes place in the eye. 



the rectilinear grid but will take the form of the barrel shaped grid 

 shown in Figure 33. By comparing the two grids it will be seen that 

 points that are equidistant on the rectilinear, as shown by the inter- 

 section of the cross lines, are not equidistant in the barrel shaped grid. 

 They are practically the same distance apart near the axis but the 

 farther away from the axis you go the smaller these distances become. 

 The effect of this is twofold. It causes straight lines that do not 

 pass through the axis of vision, to be bowed outward in their central 

 portions. It also causes objects away from the axis to be imaged in 

 smaller relative size than those near the axis. 



