Editing Holography (section)

===Apparatus===
A hologram can be made by shining part of the light beam directly into the recording medium, and the other part onto the object in such a way that some of the scattered light falls onto the recording medium. A more flexible arrangement for recording a hologram requires the laser beam to be aimed through a series of elements that change it in different ways. The first element is a [[beam splitter]] that divides the beam into two identical beams, each aimed in different directions:
* One beam (known as the 'illumination' or 'object beam') is spread using [[Lens (optics)|lenses]] and directed onto the scene using [[mirror]]s. Some of the light scattered (reflected) from the scene then falls onto the recording medium.
* The second beam (known as the 'reference beam') is also spread through the use of lenses, but is directed so that it does not come in contact with the scene, and instead travels directly onto the recording medium.

Several different materials can be used as the recording medium. One of the most common is a film very similar to [[photographic film]] ([[silver halide]] [[photographic emulsion]]), but with much smaller light-reactive grains (preferably with diameters less than 20&nbsp;nm), making it capable of the much higher [[Optical resolution|resolution]] that holograms require. A layer of this recording medium (e.g., silver halide) is attached to a transparent substrate, which is commonly glass, but may also be plastic.