Figure 2-47. Image formed by convergent lens.

TM 9-258

pound lenses (para 4-2) may be used to correct for color

point of an object is emitting cones of rays of light which

and other faults. A theoretically perfect single lens is

are incident upon the front face of the lens. Two rays

assumed in this paragraph.

from a point will be sufficient to indicate the action of the

c. Plotting the Image. To plot the formation of an

rays and to located the image of this point (fig 2-47).

image by a convergent lens, consider that every

Figure 2-47. Image formed by convergent lens.

(1) Assume that one ray from a point at the top

the two rays intersect becomes the corresponding point

of the object will pass through the center of the lens.

for the image.

Since this ray will strike the lens at the center, its path is

(2) Two similar rays from a point at the bottom

not deviated. A second ray from this point of the object

of the object form a point of the image corresponding to

strikes the lens above the axis, is refracted upon entering

the bottom of the object. Every point on the object forms

and upon leaving the optically denser medium, and

its point of light on the image in the same way. Light

intersects the first ray, For this second ray, we chose a

rays from the upper part of the object form points of light

ray parallel to the axis. After passing through the lens, it

on the lower part of the image and vice versa. The

will converge to the point of principal focus and thus can

image is transposed diametrically and symmetrically

across the optical axis from the object resulting in in-

easily

located.

The

point

where

2-33