Figure 2-69. Curvature of image .

TM 9-258

f. Rays and Pencils. A definition of eccentric and

those along the axis. Eccentric pencils are those which

pass through the lens near the rim, remote from its

paraxial rays and of centric, eccentric, and paraxial

center.

pencils will clarify curvature of image in spherical

g. Hourglass Distortion. Paraxial magnification of a

aberration. Eccentric rays are rim rays which pass

convergent lens (magnification through the lens near the

through a lens remote from its center. Paraxial rays are

optical axis) is actually less than the true magnification of

those along the axis of the lens Oblique centric pencils

the lens. Spherical aberration thus appears as hourglass

are cones of light which pass through the center of a lens

or pincushion distortion when a vertual image is viewed

at a considerable angle to the principal axis. Paraxial

through an un

pencils are

2-52