Editing Adaptive optics (section)

=== Wavefront sensing and correction ===
An adaptive optics system tries to correct these [[Optical aberration|distortions]], using a [[wavefront sensor]] which takes some of the astronomical light, a [[deformable mirror]] that lies in the optical path, and a computer that receives input from the detector.<ref>{{cite journal
 | last = Hippler
 | first = Stefan
 | title = Adaptive Optics for Extremely Large Telescopes
 | journal = [[Journal of Astronomical Instrumentation]]
 | volume = 8
 | issue = 2
 | pages = 1950001–322
 | date = 2019
 | doi = 10.1142/S2251171719500016
 | bibcode = 2019JAI.....850001H| arxiv = 1808.02693
 | s2cid = 119505402
 }}</ref> The wavefront sensor measures the distortions the atmosphere has introduced on the timescale of a few [[millisecond]]s; the computer calculates the optimal mirror shape to correct the [[Optical aberration|distortions]] and the surface of the [[deformable mirror]] is reshaped accordingly.  For example, an {{convert|8|–|10|m|cm in|adj=on}} telescope (like the [[Very Large Telescope|VLT]] or [[Keck telescope|Keck]]) can produce AO-corrected images with an [[angular resolution]] of 30–60 [[milliarcsecond]] (mas) [[Image resolution|resolution]] at [[infrared]] wavelengths, while the resolution without correction is of the order of 1 [[arcsecond]].

In order to perform adaptive optics correction, the shape of the incoming wavefronts must be measured as a function of position in the telescope aperture plane. Typically the circular telescope aperture is split up into an array of [[pixel]]s in a wavefront sensor, either using an array of small [[lenslet]]s (a [[Shack–Hartmann wavefront sensor]]), or using a curvature or pyramid sensor which operates on images of the telescope aperture. The mean wavefront perturbation in each pixel is calculated. This pixelated map of the wavefronts is fed into the deformable mirror and used to correct the wavefront errors introduced by the atmosphere. It is not necessary for the shape or size of the [[astronomical object]] to be known&nbsp;– even [[Solar System]] objects which are not point-like can be used in a Shack–Hartmann wavefront sensor, and time-varying structure on the surface of the [[Sun]] is commonly used for adaptive optics at solar telescopes. The deformable mirror corrects incoming light so that the images appear sharp.