Peter Yanczer's Pages
The Scophony System
The English Scophony system is probably the most interesting and the least
known of the scanning methods described here. In spite of the fact that without
a doubt, the Scophony systems provided the highest performance ever achieved
with mechanical scanners. In 1938, Scophony showed and successfully demonstrated
three types of 405 line mechanical television receivers at the annual Radiolympia show in
England. One was a home receiver, in a cabinet that produced a picture
approximately 24" by 22". The other two were of similar construction, but
without cabinets, intended for theater type operation. One produced a 6 by 5
foot picture and the other, 9 by 12 feet. Several of the theater models were
installed and operating successfully. None of these receivers were sold because
their production was halted due to the oncoming war in Europe. The Scophony
system consisted of several unique innovative devices working together. It used
a new "split focus" optical system coupled to a "Jeffree Cell," light modulator
and special high speed synchronous motors to drive the scanners. Each were
important fundamental Scophony inventions, developed by them for their
mechanical scanning systems.
The split focus optical system invented by G. W. Walton, was developed
specifically for use with mirror scanning systems. Focusing of light beams was
accomplished by crossed cylindrical lenses, concentrating the light in two
planes. This technique allowed the efficient use of smaller lenses and mirrors
in the optical system, thereby reducing size and cost of the scanning equipment.
This was especially important to Scophony because of their intent to produce
very large picture sizes, normally requiring large costly optic elements.
The Jeffree cell was the light modulator used in the Scophony system.
Developed in by J. H. Jeffree in 1934, it was a major improvement over the Kerr
cell, both in efficiency and ease of operation. As much as 200 times (not
percent), more modulated light was available at the screen because it had the
ability to store image elements. Its principle of operation was that if a
supersonic mechanical oscillation passes through a transparent fluid in which a
beam of light, perpendicular to the wave front is also passing, a series of
retardations and accelerations of the light beam will occur. These oscillations
in the fluid, properly controlled act much like a diffraction grating and will
cause selective cancellations of the light waves passing through the fluid. By
matching the speed of the sonic wave front through the fluid, to the speed of
the scanning beam passing through the cell, the wave front could act on the
light passing through for much longer times. This resulted in higher levels of
modulated light being passed on to the scanning mirrors. Optical devices using
the same principle of operation as the Jeffree cell have been "re-invented" in
recent years for applications in television and lasers. This was a device well
ahead of its time.
The Scophony system used two mirror drums one as a low speed scanner with 12
mirrors operating at approximately 240 RPM. A high speed scanner with 20
mirrored surfaces ran at 30,375 RPM for a 405 line transmission. When set up for
the American 441 line system, the high speed scanner turned at 39,690 RPM. These
motors were good for at least 1000 hours of use and most went many times longer
with no measurable wear. Considering that the year was 1938, this was an
outstanding accomplishment. At the same time, Scophony was developing
synchronous motors that could operate at 150,000 RPM.
The period between 1932 and 1939 was the "coming of age" for television. In
England and European countries, television as a service was developing to the
point where program content was becoming more important than the novelty of
television. These years were also the "coming of age" for mechanical systems,
and innovation was the rule. During these years, mechanical television offered
many advantages over most cathode ray systems. Important advantages like,
brighter, sharper, larger pictures. They also offered longer life, lower
maintenance costs and better reliability.
There was no popular resistance to
mechanical systems as there might be today and some receivers were being sold.
As a result, there was an ongoing effort on the part of many companies to
improve existing equipment and to develop new ideas. World War II completely
ended the activity in mechanical television but generated an intense interest in
cathode ray tubes and their associated circuits. The reason??.. It was RADAR! By
the end of the war, there had been so much progress in radar development; most
of which could be transferred directly to television, that the first commercial
receivers after the war included 15" and 20" direct view models as well as
projection sets providing newspaper sized images.
However, we are not rid of mechanical television as yet. Even today, some 75
years after John Logie Baird was able to show that dim flickering image of a
young boy on his apparatus, just about all of us continue to buy, use and
generally accept mechanical television systems in our homes. These are commonly
referred to as "VCRs". Most of us have at least one. I have three, one of which
(a Panasonic) is 16 years old and has never required service of any sort. And it
is still used almost daily. So much for reliability on mechanical systems.
Peter F. Yanczer