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Philo Farnsworth is nearly universally given
credit as the inventor of electronic television.

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His first transmission of an image via his
television system occurred in 1927, and it

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was an incredibly big deal. But his invention
had less to do with the television in your

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house, and more to do with the camera in the
studio. Today, we’ll be exploring how Philo

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Farnsworth brought television out of the realm
of mechanical contraptions and into the landscape

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of pure electronics.

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You see, the cathode ray tube, the device
which effectively is the screen of an old-style

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television, was invented in the 19th century,
decades before Farnsworth made his contribution.

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The trouble was no one had yet figured out
how to turn a CRT into a television. When

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Baird invented his mechanical television,
the holes in the spinning disc served both

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as a scanning device, creating a signal from
an image focused onto it as the holes traveled

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past, AND as a display device, reconstructing
the image as a light source duplicated the

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intensity and location of each part of the
scanning device, with the holes moving the

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light’s apparent location to recreate the
image line by line. With the CRT being pretty

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thoroughly researched, it wouldn’t take
too much imagination to create an image with

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a moving electron beam. But what was unknown
was how to use a similar device to create

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a signal to actually run a CRT display.

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As I worked out in my last video, to use a
mechanical scanning method like in the Baird

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system to achieve equivalent image quality
of a US CRT television, the scanning disc

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would have to be impractically large, and
it would have to spin impossibly fast. Even

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if the lens focused on just a 3 centimeter
wide target, a 525 line scanning disc would

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be 5 meters tall, and the edges would still
be breaking the sound barrier for 30 complete

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frames per second.

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There were other ways to use a mechanical
scanning device, though. One of these was

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the so-called “Flying Spot” system. With
these systems, a mechanical disc in front

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of an extremely bright arc lamp would project
a scanning pattern on a performer’s face,

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and a simple light sensor pointed at the performer
would measure the light reflected off of him

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or her for generating the signal, with only one spot hitting the performer at one time.

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The projection
meant the mechanical disc could produce a

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much larger image than its physical size.
The trouble with this approach, however, was

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that the performer would have to be in absolute
darkness, and you still had to work around

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the poor resolution of mechanical systems
on the receiving end. Plus, I imagine the

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strobing effect as the light shone across
your eyes was fairly unpleasant for television

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talent of the day.

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Before Baird had even demonstrated his mechanical
television, Farnsworth theorized a way to

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electronically convert an image into a transmittable
electrical signal in 1921. This is part of

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why he is often regarded as television’s
inventor. He was what you might call a prodigy,

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as in 1921 he was only 15. He grew up on a
Utah farm, and the story goes that he came

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up with his idea after observing the lines
drawn in the fields from a plow, realizing

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that by altering a line as it’s drawn over
a distance, you could make an image from a

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field of lines. Perhaps this is why to this
day, each half of an interlaced frame of video

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is called a field.

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Farnsworth submitted a patent application
in January of 1927. However, Farnsworth wasn’t

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the only person trying to build an image dissector.
In fact, the invention of television is very

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complicated and to say that one person invented
it is rather simplistic. For example, before

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Farnsworth had his image dissector worked
out, German professor Max Dieckmann and his

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student Rudolf Hell applied for a patent for….
This, in 1925. In fact, Dieckmann was among

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the first to demonstrate the display capability
of the cathode ray tube back in 1906. And

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in the following year, a Russian scientist
named Boris Rosing used a CRT with experimental

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“video” signals to create geometric shapes.
See, there was a lot of experimentation going

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on all over the world. The wikipedia entry
on the history of television, which is linked

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in the description, goes over this in much
greater detail.

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Hell and Dieckmann’s patent was granted
to them in October of 1927, but they were

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never able to produce a working model. Meanwhile,
Farnsworth transmitted the first image with

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his image dissector at his laboratory in San
Francisco on September the 7th, 1927. Farnsworth’s

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invention was very crude at this point, as
it only really transmitted a line, and not

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a whole screen of an image. However, it was
a revolutionary proof of concept. On September

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3rd, 1928, Farnsworth called a press conference,
where he declared “Good news, everyone!

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I’ve invented television”. His demonstration
of actually functional electronic television

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is generally accepted as the first, and it
is for this reason that he’s often given

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credit as the inventor of television.

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Farnsworth’s image dissector was a vacuum
tube much like a CRT, but instead of emitting

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light, the image dissector was meant to detect
it. Inside the tube was a coating of caesium

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oxide, a photosensitive material. Caesium
oxide has an interesting characteristic where

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when photons hit it, it emits electrons. This
meant that an image focused with a lens onto

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the face of an image dissector would create
a pattern of electron emissions in the shape

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and intensity of the image itself. Then, this
electron image would be scanned.

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An electron beam very much like that which
would be used to draw an image on the face

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of a CRT television receiver, would methodically
scan the face of the image dissector. Now,

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as we all know, opposite attract, and likes
repel--electrons really don’t like to hang

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out together. What happens when the electron
beam encounters an area of the image dissector

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where bright light is hitting the surface?
Well, the caesium oxide coating is itself

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producing electrons, so the electron beam
would bounce back at areas where light was

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present.

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Ordinarily, most of the beam would just be
absorbed by the oxide coating or even the

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tube’s glass. But any electrons sent by
the gun that ran into a spot already filled

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with electrons emitted from the caesium oxide
would be reflected back into the tube. The

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image dissector contained a detector of sorts
that would collect these reflected electrons.

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By amplifying the output of the detector,
a signal could be produced which corresponded

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to the exact image brightness of wherever
the beam happened to be pointing on the surface

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of the image dissector. Deflect the beam in
a raster pattern using electromagnetic fields

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from a deflection yoke, and you can scan the
whole face of the dissector and generate a

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signal from the entire image.

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Here’s a more practical demonstration of
what’s going on. This poster board represents

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the target of the scanning electron beam.
The image we’re looking to capture is a

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simple white circle. A lens is focusing that
circle onto the face of the image dissector.

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The circle of light, which moves us all, by
the way, will cause the caesium oxide coating

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to emit electrons inside the tube wherever
the light touches. We’ll represent electrons

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in red. Therefore, the circle will be filled
with red electrons. It should be noted here

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that the resemblance to the Japanese flag
was entirely accidental. It took me filling

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in over 90% of this to realize, Oh, that’s
the flag of Japan.

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Anyway, the electron gun sits behind the caesium
oxide (Pop sound) and it emits a string of

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yarn, I mean an electron beam (NES Zapper
sound effect). Deflector magnets bend the

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electron beam, and will start scanning the
image. For the first few lines, nothing extraordinary

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occurs as the electrons are just absorbed
by the target. But, once the beam reaches

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the circle, it gets deflected back because
electrons are already there. In other words,

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where the light touches, well the electrons
must never go there.

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These deflected electrons get picked up by
a collector electrode inside the tube, and

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by monitoring the output from this electrode,
you get a signal which varies in intensity

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in proportion to the brightness of the spot
the beam is currently scanning. So, reverse

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the process. Here’s a television receiver.
It’s electron beam is following along the

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same path as the one in the image dissector,
so if the scanning beam is aimed at one spot,

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the electron beam in the television set will
be pointed at the same spot. Whenever the

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dissector detects light from the circle, the
signal it produces will cause the television

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receiver to spit electrons out from its own
electron gun. This will make the phosphors

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inside the tube glow in the same places that
the dissector detected light, and at the same

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relative intensity. After the scanning is
complete, the television will have drawn that

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circle. Do that really really fast and over
and over again, and you’ve got yourself

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some mighty fine television.

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If you’re confused, and I wouldn’t blame
you if you are, it might be helpful to check

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out my previous video on how analog television
works. That video discusses the raster pattern,

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how the television synchronizes the image
coherently via triggers built into the signal,

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and more in greater detail. Hopefully you’ll
be able to see that the television camera

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tube is essentially the same thing as the
cathode ray tube in a television set, but

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with the electron beam used as a way to detect
the presence of light, rather than to reproduce

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it. You can find a link to the video down
below, or hang around until the endscreen.

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Farnsworth’s image dissector was a big deal,
but it kinda sucked. Because the beam has

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to move across the face of the dissector so
quickly in order to produce an image, it has

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only the tiniest fraction of a second to actually
encounter an electron on the surface and be

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deflected back. The caesium oxide coating
wasn’t super great at producing electrons

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from light, so television cameras that used
Farnsworth’s image dissector needed an insane

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amount of light in order to work. This meant
studio lighting was absurdly bright--and hot--,

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and it generally presented unfortunate limitations.

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A much more practical device for producing
television signals was the iconoscope. Here

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comes another person into the fold. Vladimir
Zworykin filed patents for a television system

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in 1923 and 1925. If you’ve been paying
attention, you’ll have noticed that these

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years predate Farnsworth’s patent application.
I told you this was complicated.

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In 1923, Zworykin presented his idea to H
P Davis, the general manager of Westinghouse,

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where he worked, and in 1925 he demonstrated
the first prototype. However, it barely worked,

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and Davis wasn’t impressed. So unphased
was Davis that he told Zworykin to work on

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something useful. Wwll. Zworykin would later
work for RCA.

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The iconoscope functioned essentially the
same as the image dissector, but there was

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one key difference. And Zworykin wasn’t
the one who discovered the principle that

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would solve the problem. That was Hungarian
engineer Kálmán Tihanyi. Too many people

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here.

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Anyway, the big deal with the iconoscope was
that it didn’t rely solely on electrons

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emitted from the Caesium Oxide. Rather, it
used a sheet of mica which had tiny silver

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particles coated with our friend Caesium Oxide
on one side, and a thin film of plain old

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silver on the other. The separation of these
two sheets provided by the mica essentially

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turned the thing into a giant capacitor, capable
of storing electrons.

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When operating, the iconoscope would first
send a steady sweep of electrons across the

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whole target. This would provide a uniform
charge throughout the mica sheet. Light reflected

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from subjects in the studio and subsequently
focused through a lens onto the target would

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cause the caesium oxide to emit electrons
again in the spots hit with light, creating

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an electron copy of the image, and this would
cause the charge stored between the layers

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to decay more rapidly than it would if no
light were hitting it. The next time the target

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is scanned, areas that weren’t hit with
light will still have electrons in them, which

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will resist the beam’s efforts to try and
add more. This extra beam energy is reflected

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back and picked up by the detector ring. Areas
that were hit with light would quickly lose

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their electrons, and the beam’s energy would
instead be used to replenish these lost electrons.

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The iconoscope produced an inverted signal,
as dark areas reflected the beam strongly,

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and bright areas didn’t reflect it much
at all, but it was much, much, MUCH more sensitive

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than Farnsworth’s image dissector because
it could store electrons in the mica sheet,

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and thus greatly increase the likelihood that
the electron beam would actually be deflected

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back to the detector.

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One tricky bit about the iconoscope was that
the light it was detecting and the electron

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beam had to hit the mica sheet from the same
side. This is why the tube is such a weird

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shape. The electron gun can’t be in the
line of sight of the target, so it’s tucked

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below the target screen at an angle. In a
working camera, it’s actually in the front,

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resting below the lens. Electronics in the
camera would adjust its scanning sweeps as

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it went to compensate for the keystone shape
it would naturally produce if the beam was

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projected as a simple square at an upwards
angle.

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A side effect of the way the iconoscope works
is an image that can never truly be black.

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Electrons will decay from the mica screen
without any light hitting it at all--light

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simply accelerates this decay. The detector
ring would pick these rogue electrons up,

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and it would transmit as an entirely grey
screen. There needed to be bright areas of

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the picture to pull down the average emission
of the mica screen and make the other areas

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appear black--in other words, high contrast
scenery was required. Lighting conditions

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would have to be accounted for to keep the
averaging effect of the iconoscope from producing

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odd images.

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Because this episode is a circus of who-did-what,
let’s drop one more name. The iconoscope

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design was immensely improved by accident
in 1931 when Sanford Essig left one of the

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mica plates in the oven too long. This broke
up the silver layer into tiny globules, which

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was responsible for increasing the resolution
the iconoscope could detect immensely,

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Therefore, a sharper image was produced. 
 So, don’t forget about him.

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Although the iconoscope was a great improvement
over Farnsworth’s image dissector, it still

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wasn’t that great. The images were noisy,
of poor resolution, and it still required

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a lot of light, though far less than the original
disector did. RCA would develop the Image

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Orthicon tube in the 1940’s, and this much
more sensitive device would be used into the

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1960s. The Image Orthicon tube combined principles
from the iconoscope, image dissector, and

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the original Orthicon tube.

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The Orthicon tube (along with the Eurpoean
CPS Emitron tube) contained deflector plates

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that when calibrated correctly would reduce
the velocity of scanning electrons coming

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from the electron gun to near zero as they
approached the target. This was immensely

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helpful, because without these deflectors,
electrons could still bounce back into the

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detector ring without photoelectrons being
present. This created for a noisy picture.

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Slowing the electrons down before they hit
the target meant almost no rogue electrons

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would have enough gusto to make it back to
the detector. Only those scanning electrons

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that actually encountered another electron
at the target would make their way back, as

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the extra repelling force imparted by its
photo-electric neighbor would help to push

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it backwards. This greatly reduced the grainy
image noise associated with ordinary tubes.

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In addition to the electron slow-downy thing,
the Image Orthicon tube used a neat physics

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trick to amplify the effect of the photoelectrons
and make the whole thing more sensitive. In

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an image orthicon tube, the surface the light
falls on to make the image, called the photocathode,

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and the surface the electron beam scans to
make a signal, called the target, are separated

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by a fairly great distance. The photocathode
is negatively charged, meaning electrons near

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it will want to fly away from it, and in front
of the scanning target is a wire mesh with

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a slight positive charge used to attract the
photoelectrons. This causes the photoelectrons

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emitted from the photocathode to be accelerated
towards the scanning target. The separation

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of photocathode and target causes a dramatic
increase in speed of the photoelectrons, which

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results in a multiplication of the electrons
generated from the image. This happens because

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when an individual electron slams into the
target at high speed, it causes a splash,

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forcing many electrons out of the target.
This is called secondary emission, and a wire

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mesh behind the target with a slight positive
potential traps these extra electrons. This

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phenomenon is used to greatly increase the
tube’s sensitivity.

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You see, the extra electrons produced when
the first photoelectron hit the target came

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from within the target itself. Essentially,
the high-speed of the photoelectron knocks

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out a whole bunch of electrons when it hits
the target. This causes a net loss of electrons

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in the area of impact, giving that area of
the scanning target a slight positive charge.

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When the scanning beam from the electron gun
runs over this area, the electrons it emits

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are first used to refill those lost from the
secondary emission event. The result is that

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bright areas of the picture use the beam’s
energy to recharge the target, and no electrons

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are reflected back and detected. Dark areas
of the image don’t displace electrons in

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the target, so the beam is reflected back
as electrons are already present, and a strong

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00:15:42,600 --> 00:15:46,620
signal is produced via the dynodes and electron
multiplier at the base of the tube.

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00:15:46,620 --> 00:15:50,090
The image orthicon tube was a big deal for
many reasons, not the least of which was that

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cameras could be much smaller and less awkward
as the scanning portion of the tube was no

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longer in front of the imaging target. But
it was also sensitive enough to capture scenes

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00:15:59,130 --> 00:16:03,920
lit by candlelight, and its logarithmic light
sensitivity matches that of the human eye,

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which made images produced from these tubes
appear more natural. A fun little fact immortalized

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by Wikipedia regarding the image orthicon
tube is that it’s directly responsible for

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00:16:12,880 --> 00:16:18,410
the name of the award given by the Academy
of Television Arts and Sciences. Image Orthicon

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00:16:18,410 --> 00:16:22,730
tubes were often referred to informally as
“Immys”. The presidents of the Academy

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00:16:22,730 --> 00:16:27,770
at the time, Harry Lubcke, wanted to name
the award after the Immy. But since the statuette

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00:16:27,770 --> 00:16:30,850
is female, the more feminine “Emmy” was
chosen.

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00:16:30,850 --> 00:16:35,200
The inverted signals of the image orthicon
and iconoscope--meaning bright areas produce

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00:16:35,200 --> 00:16:39,450
little to no signal and dark areas produce
a strong signal--wasn’t a problem as this

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00:16:39,450 --> 00:16:43,900
is how television broadcasts were transmitted,
anyway. It was up to your TV set to flip those

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00:16:43,900 --> 00:16:44,900
values around.

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00:16:44,900 --> 00:16:50,670
Phew. That was complicated. And I didn’t
even mention Kenjiro Takayanagi’s 1926 demonstration

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in Japan of a CRT-based television system.
Sadly he doesn’t get much credit because

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his camera was still mechanical using a Nipkow
disc. There I said it. Nip-koff. OR, should

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00:17:02,840 --> 00:17:07,179
it be nip-ko as some have suggested? I don’t
know, maybe you should argue about it in the

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00:17:07,179 --> 00:17:08,179
comments.

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00:17:08,179 --> 00:17:11,639
There are so many dots to connect here that
I’m not going to claim I got it all correct.

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For one thing, It’s hard to pin down how
developments in Europe affected those in the

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00:17:15,399 --> 00:17:20,370
US and vice versa, particularly due to the
patent dispute between Farnsworth and Zworykin

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00:17:20,370 --> 00:17:25,160
which made new developments dance around their
respective technological claims. This is a

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00:17:25,160 --> 00:17:29,741
large part of why I didn’t go into much
detail on European tubes and systems. And

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all the names given to all the tubes is very
confusing for creating a research timeline

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00:17:34,169 --> 00:17:39,039
in me head. I’m welcome to all comments
that may set records straight, so leave ‘em

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00:17:39,039 --> 00:17:43,360
below. This video is long enough, so I’ll
be ending it here. Stay tuned, as in the next

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00:17:43,360 --> 00:17:47,740
video, we’ll be looking at the next big
thing in TV--Color.

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Thanks for watching, I hope you enjoyed the
video. I am delighted at the growth this channel

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00:17:51,289 --> 00:17:54,389
is seeing and I’m glad you’re a part of
it. If you’re new to this channel, why not

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00:17:54,389 --> 00:17:57,910
hit that subscribe button? I’m doing my
best to keep videos like this headed your

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00:17:57,910 --> 00:18:00,120
way, and I’ll see you next time!

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00:18:00,120 --> 00:18:04,080
And a special thanks to supporters on Patreon.
You can support this channel through a totally

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00:18:04,080 --> 00:18:07,850
voluntary contribution by visiting my page
through the link in the description or the

250
00:18:07,850 --> 00:18:12,259
logo on our screen. With your support, you’re
helping my to make my passion of sharing technological

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00:18:12,259 --> 00:18:18,400
stories with you into a life-sustaining job,
and for that I am ever so grateful. Thank you!

252
00:18:21,920 --> 00:18:22,480
(Oh no!)

253
00:18:25,520 --> 00:18:26,020
(Well...)

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00:18:27,600 --> 00:18:29,440
(Might as well change the yarn again)