Editing Zone plate (section)

==Applications==

===Physics===
There are many [[wavelength]]s of light outside of the visible area of the [[electromagnetic spectrum]] where traditional [[Lens (optics)|lens]] materials like glass are not [[transparency (optics)|transparent]], and so lenses are more difficult to manufacture.  Likewise, there are many wavelengths for which there are no materials with a [[refractive index]] significantly differing from one.  [[X-rays]], for example, are only weakly refracted by glass or other materials, and so require a different technique for focusing.  Zone plates eliminate the need for finding transparent, refractive, easy-to-manufacture materials for every region of the [[spectrum]].  The same zone plate will focus light of many wavelengths to different foci, which means they can also be used to filter out unwanted wavelengths while focusing the light of interest.

Other waves such as sound waves and, due to [[quantum mechanics]], matter waves can be focused in the same way.  Wave plates have been used to focus beams of neutrons and helium atoms.<ref name="wmm" />

===Photography===
[[File:Christmas with zone plate.jpg|thumb|Example of an image taken with zone plate optics.]]
Zone plates are also used in [[photography]] in place of a [[photographic lens|lens]] or [[pinhole camera|pinhole]] for a glowing, soft-focus image.  One advantage over pinholes (aside from the unique, fuzzy look achieved with zone plates) is that the transparent area is larger than that of a comparable pinhole.  The result is that the effective [[f-number]] of a zone plate is lower than for the corresponding pinhole and the [[exposure (photography)|exposure time]] can be decreased. Common [[f-number]]s for a pinhole camera range from {{f/|150}} to {{f/|200}} or higher, whereas zone plates are frequently {{f/|40}} and lower. This makes hand held shots feasible at the higher ISO settings available with newer [[DSLR]] cameras.

===Gunsights===
Zone plates have been proposed as a cheap alternative to more expensive optical sights or targeting lasers.<ref>[http://www.physorg.com/news192299313.html New INL gunsight technology should improve accuracy for target shooters, hunters, soldiers], Mike Wall, Idaho National Laboratory, 5 May 2010.</ref><!-- alternative story link https://inlportal.inl.gov/portal/server.pt?open=514&objID=1269&mode=2&featurestory=DA_549448 -->

===Lenses===
Zone plates may be used as imaging lenses with a single focus as long as the type of grating used is sinusoidal in nature. A specifically designed Fresnel zone plate with blazed phase structures is sometimes called a [[kinoform]].<ref name="s853">{{cite journal | last1=Jordan | first1=J. A. | last2=Hirsch | first2=P. M. | last3=Lesem | first3=L. B. | last4=Van Rooy | first4=D. L. | title=Kinoform Lenses | journal=Applied Optics | publisher=Optica Publishing Group | volume=9 | issue=8 | date=1970-08-01 | pages=1883–1887 | issn=0003-6935 | doi=10.1364/ao.9.001883 | pmid=20094157 | bibcode=1970ApOpt...9.1883J }}</ref>

===Reflection===
A zone plate used as a reflector will allow radio waves to be focused as if by a parabolic reflector. This allows the reflector to be flat, and so easier to make. It also allows an appropriately patterned Fresnel reflector to be mounted flush to the side of a building, avoiding the wind loading that a paraboloid would be subject to.

===Software testing===
A bitmap representation of a zone plate image may be used for testing various image processing algorithms, such as:
* Image interpolation and image resampling;<ref>https://web.archive.org/web/20060827184031/http://www.path.unimelb.edu.au/~dersch/interpolator/interpolator.html Testing Interpolator Quality</ref>
* Image filtering.<ref>http://blogs.mathworks.com/steve/2011/07/22/filtering-fun/ Filtering Fun - Matlab Central</ref>
An open-source zone-plate image generator is available.<ref name="Turkowski, Ken: Zone Plate Test Pattern">https://web.archive.org/web/20200516104605/http://www.realitypixels.com/turk/opensource/#ZonePlate Zone Plate generator, C code. Archived from the [http://www.realitypixels.com/turk/opensource/index.html#ZonePlate original] on 16 May 2020.</ref>