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Another system was used in the re-release of
House of Wax, which was a side by side
format, this produced a “doorway” type of
image, which not only required a prism system
to combine the images, but also an anamorphic
(CinemaScope) lens to revert it to the correct
unsqueezed format.

Passive System.
There are two systems used for passive 3D
projection, A dual lens system, where the left
and right images are projected simultaneously
through opposing filters which separate the
Above: Re-release “side by side” squeezed print left and right images, and a single lens system,
of House of Wax which involves the projector circularly
Below: The “side by side” prism unit required for polarising alternating frames, which are
the above film.
projected at a higher frame rate to avod flicker.
In both cases, the audience have to wear glass-
es that have oppositely circular polarized lens-
es that ensures each eye sees only its
designated frame. The 3D images are
projected through similar polarising filters -
clockwise for the right eye and counter-
clockwise for the left eye. Circular
polarisation has the advantage for the viewer
in that they can move their head somewhat
without seeing double or darkened images.
In common with other polarised systems, a
The lack of standardisation meant a 3D silver screen is used to maintain the light
presentation could involve setting up polarisation and to counter some of the light
especially for the type of film that was to be losses due to the filters in both the projector
screened. and the glasses.

The introduction of digital cinema in the late RealD is the most widely used digital 3D
2000s saw a resurgence of 3D presentations. system, it alternately projects right-eye and
Digital 3D uses one of two basic 3D left-eye frames, switching between them 144
techniques - active or passive. times per second. An electro-optical liquid
crystal modulator called a Zscreen is located

14 REEL DEALS September 2021