Theatre Design & Technology - Fall 1978 - 16

Two methods have been developed for printing the film,
Komar explains. In the lensless method exposed film is
placed near print film. A single reference beam of coherent
light forms a spatial image on the print film by passing
through the exposed film. A second, optical, method employs
intermediate optics between the exposed and print films. The
spatial image formed by the coherent light passing through
the exposed film is changed by the optics into a secondary
image. This image is formed on the print film, where it interferes with the reference beam from the same laser.
The optical printing method can be used to reduce distortion of the spatial image, to change its scale, to decrease
image noise and to change a transmission hologram into a
reflection hologram in order to use film of higher sensitivity
during shooting, he writes.

Projection
For projection a specially designed holographic screen is
used. To produce it, researchers used a new silver halide
emulsion, developed in the Soviet Union, capable of resolving
10' lines per millimeter, Jeong said.
The screen, a hologram itself, multiplies spatial images
projected upon it and focuses them in air before the screen.
This is achieved through primary and secondary foci, Komar
explains. When an image falls on the zone containing the
primary focus, secondary images are formed at the zones
containing the secondary foci.
In viewing, each viewer sits at one of the foci, seeing one
image. Within the zone of the focus, the viewer may move his
or her head about 150 millimeters horizontally or vertically.
As he or she moves, the perspective for the image changes.
However, if the viewer moves out of the zone, the image
disappears, Komar writes.

Making the Screen
The screen is made in the manner of a reflection hologram,
Komar explains. One diverging beam of coherent light passes
through a compensating optical device and reaches a concave mirror. The reflected coverging beam passes through
the photoplate and converges at a point which will be the
primary focus of the screen. At the same time, several diverging beams from the same source pass through the photoplate
from the opposite side. The centers of these beams will be the
secondary foci of the screen.
The movie viewed by Jeong was projected on a screen
made by this method. He said it was about one meter square.
The system that projects the image to the screen returns
the reduced image to its original size, Jeong said. A mercury
lamp provides the illumination. The yellow line of the lamp's
emission was used, according to Jeong. The light passes
through lenses to collimate the light, through the film and
then through a large aperture lens similar to the one used
during shooting. This lens expands the image to its original
size.
In addition to the pulsed laser shooting system used to
make the movie described above, researchers at NIKFI also
have under development a system for shooting outdoors with
incoherent light, Komar reports. This camera utilizes a raster,
or "fly's eye" lens to produce multiple images on the recording film.
During shooting natural light reflected by the object passes
through the many small lenses of the raster and is focused on
the color film stock. Each lens records a different perspective
view of the object.
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Theatre Design & Technology

Komar notes that if each row of the raster contains 600 to
800 lenses, each 60 to 80 microns in diameter, viewers will
not notice the raster structure when the synthesized holographic image is projected.
Holograms of still spatial images printed from a raster
image have been made, Komar writes. He points out, though,
that the amount of depth which can be recorded is not as
great as that of the pulsed laser shooting system.
The pulsed laser system described earlier for monochromatic holographic cinematography would be modified in
several ways if multi-color images are to be made and projected.

Multi-color Imagery
In discussing the requirements for indoor multi-color
shooting, Komar explains that light of three colors would be
needed. In this case, the film would be exposed to red, blue
and green light. The lasers producing them should have impulse energies of 2 to 10 joules, coherence lengths of 10 to
20 meters and repetition rates of 16 to 24 pulses per second.
These requirements would permit shooting scenes of 10 to 20
meters in depth.
Developing lasers to produce red (wavelength: 660 nanometers) and green (wavelength: 530 nanometers) poses no
serious problems according to Komar. However, lasers producing blue light are more difficult to build, he says, although
research into pulsed dye lasers may prOVide a solution.
During shooting, each color would produce an elementary
hologram grating on the film. Each grating would contain
information on the brightness of the object for a single wavelength, Komar writes.
For projection of multi-color spatial images, the projection
screen would have to be made from a thick emulsion layer
which had been exposed to red, green and blue light.
Projection illumination for multi-color spatial images would
come from lasers producing coherent light of three or four
wavelengths, although use of these would lead to the appearance of speckle. Komar suggests the use of quasi-incoherent
light sources such as the mercury-cadmium lamp used in the
monochromatic holographic movie projection system. In this
instance parts of four wavelengths would be used to project
the spatial images. This method would also give high levels of
brightness, Komar states.
Concerning distortion of images in the monochromatic and
color systems, Komar reports that it can be reduced to acceptable levels. Parasitic images or "ghosts" which appear
during projection can be tolerated if they are equal to or less
than the attainable level of two per cent image brightness.
Interestingly, Komar points out that in color spatial image
recording and projection using multiple wavelengths, the degree of color distortion is no worse than that in ordinary color
films.
The multi-color lenticular pictures were equally impressive
to Jeong. He said he saw "a red rose with green leaves
projecting out in front of the plate."
Jeong also pointed out that although the NIKFI work is
innovative, most of the principles and methods used are
known in the U.S. However, researchers in this country have
not yet developed an emulsion with the characteristics
needed to make a holographic screen.
"I think not enough competent people have been put to
work on developing a good photosensitive material," he said,
adding that American film manufacturers see no large market
for such a film.
USITT /Fall. 1978

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