Fig. 29. a. Intensity in diffused image of a point. b. Intensity in diffused image of a line. c. Spread function or light distribution in image of a sharp edge. d. Bar targets of various spatial frequencies (N lines per millimeter) have periods of 1/N mm. e. Ideal images of the bar targets would be square waves; because of the spread function, the light distribution in the image is sinusoidal. As the spatial frequency of the bar target is increased, the contrast in the image is reduced. f. Modulation transfer function for two lenses. (Smith WJ: Modern Optical Engineering. New York: McGraw-Hill, 1966.)