<P> Like conventional photography, holography requires an appropriate exposure time to correctly affect the recording medium . Unlike conventional photography, during the exposure the light source, the optical elements, the recording medium, and the subject must all remain perfectly motionless relative to each other, to within about a quarter of the wavelength of the light, or the interference pattern will be blurred and the hologram spoiled . With living subjects and some unstable materials, that is only possible if a very intense and extremely brief pulse of laser light is used, a hazardous procedure which is rare and rarely done outside of scientific and industrial laboratory settings . Exposures lasting several seconds to several minutes, using a much lower - powered continuously operating laser, are typical . </P> <P> 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: </P> <Ul> <Li> One beam (known as the illumination or object beam) is spread using lenses and directed onto the scene using mirrors . Some of the light scattered (reflected) from the scene then falls onto the recording medium . </Li> <Li> The second beam (known as the reference beam) is also spread through the use of lenses, but is directed so that it doesn't come in contact with the scene, and instead travels directly onto the recording medium . </Li> </Ul> <Li> One beam (known as the illumination or object beam) is spread using lenses and directed onto the scene using mirrors . Some of the light scattered (reflected) from the scene then falls onto the recording medium . </Li>

How do different frequencies of light affect a recorded video image