The diffraction limit of a telescope or similar optical device is the minimum angle between two objects that can be clearly distinguished. The diffraction limit is determined by the diameter of the telescope and the wavelength of the light being observed.
Definition
Diffraction is the term used to describe the phenomenon of a wave bending around an object, or spreading (propagating) after passing through a gap. It is most noticeable if the object or gap is about the same size as the wavelength of the wave.
Photography
The diffraction limit can be an important concept in photography. Decreasing the size of a camera's aperture--the opening that admits light--increases the depth of field and sharpness of the image produced. Eventually, however, the aperture becomes so small that softening of the image by diffraction becomes the limiting factor.
Negative Index
Several technologies have been developed to beat the classical diffraction limit. Among these are so-called "negative index" materials, which refract light in the opposite direction of normal media.
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