Diffraction-limited system

In <a href="/facts/Optics/p0vq4S1T">optics</a>, any <a href="/facts/Optical_instrument/jB29DQNk">optical instrument or system</a> – a <a href="/facts/Microscope/ldJp0CI3">microscope</a>, <a href="/facts/Telescope/BDwYahhR">telescope</a>, or <a href="/facts/Camera/j4uqsfJQ">camera</a> – has a principal limit to its <a href="/facts/Optical_resolution/TcLkPYFw">resolution</a> due to the <a href="/facts/Physics/a7aH2y08">physics</a> of <a href="/facts/Diffraction/Mk80xXHT">diffraction</a>. An optical instrument is said to be diffraction-limited if it has reached this limit of resolution performance. Other factors may affect an optical system's performance, such as lens imperfections or <a href="/facts/Optical_aberration/YIqd9cA8">aberrations</a>, but these are caused by errors in the manufacture or <a href="/facts/Paraxial_approximation/Mj2XrtWm">calculation</a> of a lens, whereas the diffraction limit is the maximum resolution possible for a theoretically perfect, or ideal, optical system.
The diffraction-limited <a href="/facts/Angular_resolution/wJarPBWF">angular resolution</a>, in radians, of an instrument is proportional to the <a href="/facts/Wavelength/kcJU0ymz">wavelength</a> of the light being observed, and inversely proportional to the diameter of its <a href="/facts/Objective_(optics)/6smChS48">objective</a>'s <a href="/facts/Entrance_pupil/8KSLrjSJ">entrance aperture</a>. For telescopes with circular apertures, the size of the smallest feature in an image that is diffraction limited is the size of the <a href="/facts/Airy_disk/eDdnH4AQ">Airy disk</a>. As one decreases the size of the aperture of a telescopic <a href="/facts/Lens_(optics)/ejlH6n5c">lens</a>, diffraction proportionately increases. At small apertures, such as <a href="/facts/F-stop/QcdW0077">f/22</a>, most modern lenses are limited only by diffraction and not by aberrations or other imperfections in the construction.
For microscopic instruments, the diffraction-limited <a href="/facts/Spatial_resolution/ll8LNYxN">spatial resolution</a> is proportional to the light wavelength, and to the <a href="/facts/Numerical_aperture/EvW1oVBC">numerical aperture</a> of either the objective or the object illumination source, whichever is smaller.
In <a href="/facts/Astronomy/0ArJVM1p">astronomy</a>, a diffraction-limited observation is one that achieves the resolution of a theoretically ideal objective in the size of instrument used. However, most observations from Earth are <a href="/facts/Astronomical_seeing/TdVzedKJ">seeing</a>-limited due to <a href="/facts/Atmosphere_of_Earth/FV97Am25">atmospheric</a> effects. Optical telescopes on the <a href="/facts/Earth/HLLmDfj0">Earth</a> work at a much lower resolution than the diffraction limit because of the distortion introduced by the passage of light through several kilometres of <a href="/facts/Turbulence/NpgFUhG5">turbulent</a> atmosphere. Advanced observatories have started using <a href="/facts/Adaptive_optics/D1vWeHK0">adaptive optics</a> technology, resulting in greater image resolution for faint targets, but it is still difficult to reach the diffraction limit using adaptive optics.
<a href="/facts/Radio_telescope/SxIXUowL">Radio telescopes</a> are frequently diffraction-limited, because the wavelengths they use (from millimeters to meters) are so long that the atmospheric distortion is negligible. Space-based telescopes (such as <a href="/facts/Hubble_Space_Telescope/NQeIf0vw">Hubble</a>, or a number of non-optical telescopes) always work at their diffraction limit, if their design is free of <a href="/facts/Optical_aberration/YIqd9cA8">optical aberration</a>.
The beam from a <a href="/facts/Laser/jk6PTvvT">laser</a> with near-ideal beam propagation properties may be described as being diffraction-limited. A diffraction-limited laser beam, passed through diffraction-limited optics, will remain diffraction-limited, and will have a spatial or angular extent essentially equal to the resolution of the optics at the wavelength of the laser.

Diffraction-limited system open-in-new

Diffraction-limited system