Editing Point spread function (section)

== Applications ==
=== Microscopy ===
[[File:63x 1.4NA Confocal Point Spread Function 2+3D.png|thumb|An example of an experimentally derived point spread function from a confocal microscope using a 63x 1.4NA oil objective. It was generated using Huygens Professional deconvolution software. Shown are views in xz, xy, yz and a 3D representation.]]
In microscopy, experimental determination of PSF requires sub-resolution (point-like) radiating sources. [[Quantum dot]]s and [[fluorescent]] [[bead]]s are usually considered for this purpose.<ref>Light transmitted through minute holes in a thin layer of silver  vacuum or chemically deposited on a slide or cover-slip have also been used, as they are bright and do not photo-bleach.
{{cite book
 | title = Methods in Enzymology: Measuring biological responses with automated microscopy, Volume 414
 | chapter = Tracking individual proteins in living cells using single quantum dot imaging
 | editor = James Inglese
 | author1 = S. Courty
 | author2 = C. Bouzigues
 | author3 = C. Luccardini
 | author4 = M-V Ehrensperger
 | author5 = S. Bonneau
 | author6 = M. Dahan
 | name-list-style = amp
 | publisher = Academic Press
 | year = 2006
 | isbn = 978-0-12-182819-6
 | pages = [https://archive.org/details/methodsinenzymol414ingl/page/223 223–224]
 | chapter-url = https://books.google.com/books?id=5bczPeokiqAC&pg=PA223
 | url-access = registration
 | url = https://archive.org/details/methodsinenzymol414ingl/page/223
 }}</ref><ref>
{{cite journal
 | journal = Journal of Microscopy
 | title = The point-spread function of a confocal microscope: its measurement and use in deconvolution of 3-D data
 | author1=P. J. Shaw  |author2=D. J. Rawlins
 | name-list-style=amp | volume = 163
 | issue = 2
 | pages = 151–165
 | date = August 1991
 | doi=10.1111/j.1365-2818.1991.tb03168.x
 | s2cid = 95121909
 }}</ref> 
Theoretical models as described above, on the other hand, allow the detailed calculation of the PSF for various imaging conditions. The most compact [[diffraction limited]] shape of the PSF is usually preferred. However, by using appropriate optical elements (e.g., a [[spatial light modulator]]) the shape of the PSF can be engineered towards different applications.

=== Astronomy ===
[[File:Hubble PSF with flawed optics.jpg|thumb|The point spread function of [[Hubble Space Telescope]]'s [[Wide Field and Planetary Camera|WFPC]] camera before corrections were applied to its optical system.]]

In [[observational astronomy]], the experimental determination of a PSF is often very straightforward due to the ample supply of point sources ([[star]]s or [[quasars]]). The form and source of the PSF may vary widely depending on the instrument and the context in which it is used.

For [[radio telescopes]] and [[Diffraction-limited system|diffraction-limited]] space [[telescopes]], the dominant terms in the PSF may be inferred from the configuration of the aperture in the [[Fourier domain]].  In practice, there may be multiple terms contributed by the various components in a complex optical system. A complete description of the PSF will also include diffusion of light (or photo-electrons) in the detector, as well as [[Spacecraft attitude control|tracking]] errors in the spacecraft or telescope.

For ground-based optical telescopes, atmospheric turbulence (known as [[astronomical seeing]]) dominates the contribution to the PSF. In high-resolution ground-based imaging, the PSF is often found to vary with position in the image (an effect called anisoplanatism). In ground-based [[adaptive optics]] systems, the PSF is a combination of the aperture of the system with residual uncorrected atmospheric terms.<ref>{{Cite web|url=http://www.telescope-optics.net/diffraction_image.htm|title=POINT SPREAD FUNCTION (PSF)|website=www.telescope-optics.net|access-date=2017-12-30}}</ref>

=== Lithography ===
[[File:Airy_spot_overlap.png|thumb|left|300px|'''Overlapped PSF peaks.''' When the peaks are as close as ~ 1 wavelength/NA, they are effectively merged. The FWHM is ~ 0.6 wavelength/NA at this point.]]
The PSF is also a fundamental limit to the conventional focused imaging of a hole,<ref name=nat_res>[http://www.lithoguru.com/scientist/litho_tutor/TUTOR23%20(Fall%2098).pdf The Natural Resolution]</ref> with the minimum printed size being in the range of 0.6-0.7 wavelength/NA, with NA being the [[numerical aperture]] of the imaging system.<ref>[https://www.weizmann.ac.il/mcb/ZviKam/ALM/L2_Resolution.pdf Principles and Practice of Light Microscopy]</ref><ref>[http://ww.lithoguru.com/scientist/litho_papers/2000_103_Corner%20Rounding%20and%20Line-end%20Shortening%20in%20OL.pdf Corner Rounding and Line-end Shortening]</ref> For example, in the case of an [[extreme ultraviolet lithography|EUV]] system with wavelength of 13.5 nm and NA=0.33, the minimum individual hole size that can be imaged is in the range of 25-29 nm. A [[phase-shift mask]] has 180-degree phase edges which allow finer resolution.<ref name=nat_res/>

=== Ophthalmology ===

Point spread functions have recently become a useful diagnostic tool in clinical [[ophthalmology]].  Patients are measured with a [[Shack–Hartmann wavefront sensor|Shack-Hartmann]] [[wavefront sensor]], and special software calculates the PSF for that patient's eye. This method allows a physician to simulate potential treatments on a patient, and estimate how those treatments would alter the patient's PSF. Additionally, once measured the PSF can be minimized using an adaptive optics system. This, in conjunction with a [[Charge-coupled device|CCD]] camera and an adaptive optics system, can be used to visualize anatomical structures not otherwise visible ''in vivo'', such as cone photoreceptors.<ref>{{Cite journal|last1=Roorda|first1=Austin|last2=Romero-Borja|first2=Fernando|last3=Iii|first3=William J. Donnelly|last4=Queener|first4=Hope|last5=Hebert|first5=Thomas J.|last6=Campbell|first6=Melanie C. W. |author6-link=Melanie Campbell|date=2002-05-06|title=Adaptive optics scanning laser ophthalmoscopy|journal=Optics Express|language=EN|volume=10|issue=9|pages=405–412|doi=10.1364/OE.10.000405|issn=1094-4087| bibcode=2002OExpr..10..405R |pmid=19436374|s2cid=21971504|doi-access=free}}</ref>