Figure 2-70. Diffraction pattern, greatly magnified .

TM 9-258

c. In practice, the resolving power of a lens

selected for a specific purpose is usually so great that

any lack of sharpness of detail is too slight to be

observed and, therefore, too slight to be objectionable in

the performance of the service for which the lens is

intended.

2-44. Newton's Rings.

a. When position (convergent) and negative

(divergent) lenses of slightly unequal curvature are

pressed one against the other, irregular bands or

patches of color appear between the surfaces. This

pattern is called Newton's rings (fig 2-71) after Sir Issac

Newton who directed attention to it. This condition is a

defect if it occurs in a compound lens. It may be utilized

to advantage as a means for testing the accuracy of

grinding and polishing lenses.

Figure 2-71. Newton's rings .

2-54