Editing Holography (section)

===Point sources===
[[File:Zonenplatte Cosinus.png|upright|thumb|Sinusoidal zone plate]]

If the recording medium is illuminated with a point source and a normally incident plane wave, the resulting pattern is a [[Zone plate|sinusoidal zone plate]], which acts as a negative [[Fresnel lens]] whose focal length is equal to the separation of the point source and the recording plane.

When a plane wave-front illuminates a negative lens, it is expanded into a wave that appears to diverge from the focal point of the lens. Thus, when the recorded pattern is illuminated with the original plane wave, some of the light is diffracted into a diverging beam equivalent to the original spherical wave; a holographic recording of the point source has been created.

When the plane wave is incident at a non-normal angle at the time of recording, the pattern formed is more complex, but still acts as a negative lens if it is illuminated at the original angle.