Duplex process
In film technology, there are, in addition to the simplex process, the duplex process and also various triplex processes.
In the simplex process, the phase images are recorded and played back in the order 1, 2, 3, 4, 5, 6, 7, 8 etc. with a film drive . During the film transport there is a dark phase created by a rotating shutter. The moving picture flickers.
The annoying flicker can be switched off with the duplex process . The phase images are displayed alternately with two film drives, with the odd-numbered images running through one mechanism and the even-numbered images running through the other. The images on the screen are brought into congruence with two lenses and a stationary phase image is projected with a suitable aperture, while the next is hidden in position. The screen is continuously illuminated. The frame rate of each mechanism is half that of the simplex method.
Max Skladanowsky used the duplex method with his bioscope in 1895, William Green used it in 1896 for John Alfred Prestwich . Skladanowsky is the two-strip duplex, while Green is the single-strip duplex. The even-numbered images on a film are arranged offset from the odd-numbered ones around the so-called duplex parallax and interlaced with one another. The duplex parallax is always an odd number of film steps .
The single stripe sequence can look like this: 1-empty-3-2-5-4-7-6-9-8-11-10-etc.
In 1923 Alcide Viviani obtained a patent for the single-strip duplex process, although it was actually no longer patentable at the time.
Main advantage
With the duplex method, you can choose any image frequency, down to a standstill, one phase image comfortably pushes the other away. The prerequisite for this are two light sources that shine as evenly and equally as possible.
Triplex processes are used for certain color film systems.
literature
- Brevet Français, No 505 556
- Brevet Français, No 565 540
- U.S. Patent 970,199, dated September 13, 1910