28 AMES, PROCTOR AND AMES. 



This effect applies to all objects depending in amount upon their 

 angular obliquity regardless of their distance away. 



This distortion is very easily seen by looking at the middle of any 

 rectilinearly bounded space such as the side of a room and, without 

 allowing the axis of vision to change, noting the curvature of the bound- 

 ary lines. 



It is in fact the most easily noticed of the characteristics of our 

 retinal picture. 



SUMMARY. 



The effect of this distortion on the nature of the images of objects 

 off the axis is very marked. It causes straight lines in a scene to be- 

 come curved and take very different positions relative to each other 

 from those laid down by the laws of disappearing perspective. At the 

 same time it causes objects to one side of the line of vision to become 

 relatively smaller. 



In corrected photographic lenses this distortion is corrected so that 

 with such a lens a photograph of the rectilinear grid shown in Figure 33 

 would also be rectilinear with all the squares the same shape and size. 

 Figure 34, which is a photograph taken with a lens having the same 

 distortion as the eye, shows the characteristic barrel distortion while 

 Figure 35 shows the same scene taken with a corrected lens. The 

 barrel distortion is shown in Figure 3-4 in the curvature of the lines in 

 the tiling, of the edge of the tank and of the balcony. This distortion 

 produces a more natural effect. This is most noticeable by comparing 

 the ceilings in the two photographs. That in Figure 34 seems to arch 

 over properly, while that in Figure 35 flares upward. It is also evi- 

 dent in the way the lower left hand corner of the tank is rendered. By 

 comparison the corner in Figure 35 seems to fall away and gives the 

 effect of the water not being level. 



It is of the greatest interest and significance, that of all the charac- 

 teristics of the retinal picture distortion has been most commonly used 

 by the great painters. That the " rectilinear" effect is not satisfactory 

 has long been recognized. W. R. Ware in his book 10 on perspective in 

 a chapter entitled " Cylindrical, Curvilinear or Panoramic Perspective" 

 points out that the laws of ordinary disappearing perspective must be 

 departed from in order that the depicting of certain features on the 

 sides of the field of view shall appear satisfactory. He shows this is 

 especially necessary in the case of certain architectural compositions, 



io Modern Perspective, W. R. Ware, University Press, Cambridge, Mass. 



