Diffraction results from the finite wavelength of a light wave. Due to diffraction, the image of a point object is no longer a point even if the optical system is
perfect. Every optical system is affected by diffraction; therefore, a diffraction‐limited optical system actually means a perfect optical system (because its imaging performance is only limited by diffraction). As will be shown in Chapter 6, diffraction determines the ultimate resolution that can be achieved by an optical imaging system.
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