**4. Laser transmission hologram**

The space represented in the laser transmission image extends from the entire surface of the holographic plate back to the extremities of the subject, exactly in the same way that a windowpane acts as a boundary to a view. This is also true for one step optical reflection holograms.The free viewing zone is the same as viewing an object from any vantage point in through a window, the viewing zone is 180 degrees horizontally and vertically from the plate. The image can be seen just as easily from near or far. The space is unfocused and undistorted – it is an exact spatial replica of the subject and elicits perceptual cues of the physiological type which are precisely in accord with the perception of real objects.

The one- to- one scale of the representation of space occurs at a resolution higher than is perceptible by the human visual system. Other representational systems use scaling, whereby the original image is larger, distorted or smaller than the original subject. All the sources for information of depth come to the beholder as they would for a real world object separated by a piece of glass, in particular the physiological cues of accommodation and fusion which are critical at close range. It stands to reason that a key effect of the one step optical transmission holograms representational system is a strong phenomenological link to its real-world referent.

The dominant textural property of laser transmission holograms is the grainy quality of laser light known as laser speckle. This minute dotting in three-dimensional volume lends a somewhat worn, aged, yet constantly mobile micro surface to all image elements. A correspondence between physiological operations of the eye in the perception of laser speckle and the need for alterations in aperture of the camera in documenting laser transmission holograms can be deduced from Graham Saxby's explanation:

Laser viewable holograms are particularly difficult to photograph successfully owing to the presence of obtrusive speckle and to the very high contrast they often possess… the speckle size is large and more obtrusive for small lens apertures and in order to minimize the effect it is important to use the largest possible lens aperture (Saxby, 1988).

To the beholder it may seem that the real-time movement of the laser speckle directly reflects the constant shifting of their eyes. This gives the effect of a deep silence, which Karl Frederick Reuterswald refers to in his finger language – the silent movement of fish in an aquarium.

Holographic space has its own time and depth; yet it also has a profound silence, as in an aquarium. To me the silence of the aquarium is more impressive than the colour or the movement of the fish (Reuterswald, 1989).

Laser transmission holograms are generally monochromatic and replayed in the same wavelength in which they were recorded though they can be full colour by using a combination of lasers to record and replay.
