(Science: microscopy) The image of a bright point object as focused by a lens system. With monochromatic light, it consists of a central point of maximum intensity surrounded by alternate circles of light and darkness caused by the reinforcement and interference of diffracted rays. The light areas are called maxima and the dark areas minima. The distribution of light from the centre to the outer areas of the figure was investigated mathematically by Sir George airy. The diffraction disk forms a basis for determining the resolving power of an ideal lens system. The diameter of the disk depends largely on the aperture of the lens. The diffraction of light causing the airy disk is a factor limiting the resolution of a well corrected optical system.
The bright disk of light (surrounded by alternating dark and bright diffraction rings)that is formed by a perfect diffraction-limited lens, focusing an image of an infinitely small source of light. For a minute absorbing spot, the diffraction pattern is a dark airy disk surrounded by brighter and darker diffraction rings. Since the airy disk is the smallest unit that makes up the image of a luminous or absorbing object (formed by a properly corrected microscope lens in focus), the radius of the disk determines the limit of resolution of the microsc