**6. Diffractive screens applied to holographic cinematography**

To obtain holographic-like images employing incoherent light it is common to mount a set of discrete images in sequence giving the illusion of a continuous parallax system. The first example was maybe from Lloyd Cross with his integral hologram of 1972 (9), made of more than one hundred pictures acquired by means of a laterally translating movie camera. Many views are necessary to cover a wide parallax angle. We may calculate that by considering that the pupil's eye is about 3 mm wide and that it must pass from one observation region to its neighbor region without perception of a discontinuous jump when following any point in the image.

Holography is the only recording system which provides continuous parallax. A holographic image can be enlarged by means of a concave mirror, for example, but the viewing zone is restricted to only one observer and the longitudinal magnification is always different from the transverse one. The way to cinematography was paved by Komar (10), who succeeded in projecting a large size holographic image by means of a diffractive screen. He recorded a large size scene of about 1 m x 1 m, capable of including a person, through a large aperture objective (200 mm) having also a large angular aperture on a 70 mm format film. Reconstructing by inverting the direction of the reconstruction beam puts the image at the precise position occupied by the object, enabling the correction of distortions or aberrations. But this image cannot be seen by an observer because he must receive the rays in a position from which the image has a reversed depth and can only receive rays coming from the aperture of the lens, much smaller than the whole scene. A conventional diffusing screen would only show a plane image. A diffracting screen made as the hologram of a concave mirror (11) may direct each of the viewpoints on the scene to a continuous viewpoint sequence and, through the proper managing of the diffraction order in a horizontal direction, invert the depth, showing an orthoscopic image. Multiple exposures with changing reference beam angles give the possibility to provide full parallax to more than one observer.

diffuse light vertically for the observer to see the whole projected image can then be obtained by making the hologram of a rectangular shape diffuser. The converging image which results from illuminating in a direction which is opposite to that corresponding to the reference beam occupies the zone where one observer's eye must be located. And the focusing property of the screen generates another observation zone for the other eye, provided that the angular separation of the two projectors to one screen point matches the binocular separation for the observer, obtaining by diffraction the effect of Ivanov's screen

It was conceived as a thick (Lippmann-Bragg-Denisyuk) hologram to avoid the simultaneous viewing of more than one image due to the spectral dispersion, so that the proposed solution was purely monochromatic. It still presents two of Ivanov's screen problems: different angular separation for binocular vision at different distances from the screen and the observer having to keep his head at an almost fixed position. While adding the lack of poly-chromaticity, it dispenses with a three-chromatic procedure to be applied

To obtain holographic-like images employing incoherent light it is common to mount a set of discrete images in sequence giving the illusion of a continuous parallax system. The first example was maybe from Lloyd Cross with his integral hologram of 1972 (9), made of more than one hundred pictures acquired by means of a laterally translating movie camera. Many views are necessary to cover a wide parallax angle. We may calculate that by considering that the pupil's eye is about 3 mm wide and that it must pass from one observation region to its neighbor region without perception of a discontinuous jump when following any point

Holography is the only recording system which provides continuous parallax. A holographic image can be enlarged by means of a concave mirror, for example, but the viewing zone is restricted to only one observer and the longitudinal magnification is always different from the transverse one. The way to cinematography was paved by Komar (10), who succeeded in projecting a large size holographic image by means of a diffractive screen. He recorded a large size scene of about 1 m x 1 m, capable of including a person, through a large aperture objective (200 mm) having also a large angular aperture on a 70 mm format film. Reconstructing by inverting the direction of the reconstruction beam puts the image at the precise position occupied by the object, enabling the correction of distortions or aberrations. But this image cannot be seen by an observer because he must receive the rays in a position from which the image has a reversed depth and can only receive rays coming from the aperture of the lens, much smaller than the whole scene. A conventional diffusing screen would only show a plane image. A diffracting screen made as the hologram of a concave mirror (11) may direct each of the viewpoints on the scene to a continuous viewpoint sequence and, through the proper managing of the diffraction order in a horizontal direction, invert the depth, showing an orthoscopic image. Multiple exposures with changing reference beam angles give the possibility to provide full parallax to more

The idea was patented (8), but I do not know if any prototype was made.

**6. Diffractive screens applied to holographic cinematography** 

by refraction and reflection.

for color reproduction.

in the image.

than one observer.

In that way a Lippman-Bragg-Denisyuk hologram was made for the screen and its evolution made it capable of rendering color images by means of the three-chromatic procedure. It was discontinued, but constituted the only cinema system that can receive the academic term of "holographic", because recording was made by interference of the object light (a sequence of laser pulses) with a reference beam, recording and diffraction followed, and the concept of a holographic screen was introduced, giving continuous parallax and allowing the observer to move his head. The only visual shortcoming maybe came from the strict monochromaticity of the laser light beams. Living subjects were reproduced. The system cost was, of course, very high. While in need of more precise information, it was certain that at least eight people could watch a twenty minutes movie on the 1 m x 1 m square screen at a few meters distance.
