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in front of the projector lens and polarises The shutters are synchronised with the screen
alternate frames, clockwise for the right eye images by an infrared signal that is transmitted
and counter-clockwise for the left eye. from the screen area and picked up by a sensor
in the glasses.
The Dolby 3D system uses a special alternate
colour wheel in the projector, which projects The digital cinema projector alternately
the images destined for the left and right eye at projects the right eye frame and left eye frame,
a different wavelength. The 3D glasses incor- switching between them at a high frame rate to
porate a corresponding wavelength filter for reduce flicker. Because the system does not
each eye, providing separation of the left and use polarised glasses for left-right separation,
right images. The idea is known as wave- the use of a traditional white screen is possible.
length multiplex visualisation. The advantage
of the Dolby system is that a regular white Today’s cinema goer has had a variety of 3D
screen can be used. films offered since its resurgence. The years
2012 to 2016 saw large numbers of 3D films
Active Shutter offered, but subsequent years have seen a
decline in releases.
This method of 3D uses glasses which
incorporate liquid crystal shutters, which open Many of the films were offered in both 3D and
and close in synchronism with the alternating regular versions. The requirement to wear
left and right eye images projected onto the special glasses, plus the usual extra charge
screen, effectively closing off one eye at a often saw the regular version outperform the
time. The glasses are thicker and heavier than 3D version at the box office.
polarised glasses, due to the electronics and
the battery required to make them function. The future of 3D is hard to tell. Until someone
comes up with a method of producing a 3D
Below: The very poplar Avatar was available in image without the need to wear glasses, there
both 3D and standard versions. will always be some resistance to the full scale
adoption of the system.

* The Selsyn motor was developed in the
1920s, comprised of two units, similar to
regular electric motors, connected to each
other by a cable. The basic principle was
that what ever one did, the other did the
same. That way, synchronisation between
the two projectors was maintained without
the need of cumbersome and often
dangerous mechanical linking.

This article first appeared in CinemaRecord,
the quarterly magazine of the Cinema and
Theatre Historical Society of Australia Inc.

Film frames and equipment are from the
author’s collection.

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