
ABERRATIONS 121
Figure 5.5 Distortion. The left panel shows an object consisting of straight lines. The center
panel shows barrel distortion, and the right panel shows pincushion distortion.
XX
1
Y
1
Y
Figure 5.6 Coma. The image is tilted by an amount proportional to hρ
2
cos
2
φ. The paraxial
image is at the vertex of the V.
distortion. Objects at increasing distance, x, from the axis suffer a greater shift in their position,
proportional to the cube of x. The result is a distortion of the image; the magnication is not
uniform. In this case, the apparent magnication varies with radial distance from the center.
Straight lines in the object are not imaged