Original: It might appear at first sight that a hologram could not be made using a recording medium whose thickness is much greater than the wavelength of the light used to make the hologram , because the interference pattern recorded will now be three dimensional and its structure will vary significantly with hologram depth so that it can not give rise to a single reconstructed object beam .
Simplified: To look at a hologram just recorded , you have to light the film with the reference wave . These waves are reflected on the film ( hologram ) and create ( within the proper angle of sight ) a virtual picture of the recorded object .