philo farnsworth is nearly universally
given credit as the inventor of
electronic television his first
transmission of an image via his
television system occurred in 1927 and
it was an incredibly big deal but his
invention had less to do with the
television in your house and more to do
with the camera in the studio today
we'll be exploring how Philo Farnsworth
brought television out of the realm of
mechanical contraptions and into the
landscape of pure electronics you see
the cathode ray tube the device which
effectively is the screen of an
old-style television was invented in the
19th century decades before Farnsworth
made his contribution the trouble was no
one had yet figured out how to turn a
CRT into a television when Baird
invented his mechanical television
system the holes in the spinning disk
served both as a scanning device
creating a signal from an image focused
on to it as the holes traveled past and
as a display device reconstructing the
image as a light source duplicated the
intensity and location of each part of
the scanning device with the holes
moving the lights apparent location to
recreate the image line by line with the
CRT being pretty thoroughly researched
it wouldn't take too much imagination to
create an image with a moving electron
beam but what was unknown was how to use
a similar device to create a signal to
actually run a CRT display as I worked
out in my last video to use a mechanical
scanning method like in the Baird system
to achieve equivalent image quality of a
u.s. CRT television the scanning disk
would have to be in practically large
and it would have to spend impossibly
fast even if the lens focused on just a
three centimeter wide target a 525 line
scanning disc would be five meters tall
and the edges would still be breaking
the sound barrier for 30 complete frames
per second there were other ways to use
a mechanical scanning device though one
of these was the so-called flying spot
system with these systems a mechanical
disk in front of an extremely bright arc
lamp would project a scanning pattern on
a performers face and a simple light
sensor pointed at the performer would
measure the light reflected off him or
her for generating the signal with only
one spot hitting the performer at one
time the projection meant the mechanical
disk had produced a much larger image
than his physical size the trouble with
this approach however was that the
performer would have to be in absolute
darkness and you still had to work
around the poor
resolution of mechanical systems on the
receiving end plus I imagine the
strobing effect as the light shone
across your eyes was fairly unpleasant
for television talent of the day before
Baird had even demonstrated his
mechanical television Farnsworth
theorized the way to electronically
convert an image into a transmittable
electrical signal in 1921 this is part
of why he's often regarded as
televisions inventor he was what you
might call a prodigy as a 1921 he was
only 15 he grew up on a Utah farm and
the story goes that he came up with his
idea after observing the lines drawn in
the field from a plow realizing that by
altering a line as it's drawn over a
distance you can make an image from a
field of lines perhaps this is why to
this day each half of an interlaced
frame of video is called a field
Farnsworth submitted a patent
application in January of 1927 however
Farnsworth wasn't the only person trying
to build an image dissector in fact the
invention of television is very
complicated and to say that one person
invented it is rather simplistic for
example before Farnsworth had his image
dissector worked out German professor
max dieckmann and his student Rudolph
hell applied for a patent for this in
1925 in fact dieckmann was among the
first to demonstrate the display
capability of the cathode ray tube back
in 1906 and in the following year a
Russian scientist named Boris rosing
used the CRT with experimental video
signals to create geometric shapes see
there was a whole lot of experimentation
going on all over the world the
Wikipedia entry on the history of
television which is linked in the
description goes over this in much
greater detail he'll indictments patent
was granted to them in October of 1927
but they were never able to produce a
working model meanwhile Farnsworth
transmitted the first image with his
image dissector at his laboratory in San
Francisco on September the 7th 1927
Farnsworth's invention was very crude at
this point as it only really transmitted
a line and not a whole screen of an
image however it was a revolutionary
proof-of-concept on September the 3rd
1928 Farnsworth called a press
conference where he declared good news
everyone I've invented television his
demonstration of actually functional
electronic television is generally
accepted as the first and it is for this
reason that he's often
giving credit as the inventor of
television Farnsworth's image dissector
was a vacuum tube much like a CRT but
instead of emitting light the image
dissector was meant to detect it inside
the tube was a coating of cesium oxide a
photosensitive material cesium oxide has
an interesting characteristic where when
photons hit it it emits electrons this
meant that an image focused with a lens
onto the face of an image dissector
would create a pattern of electron
emissions in the shape and intensity of
the image itself then this electron
image would be scanned an electron beam
very much like that which would be used
to draw an image on the face of a CRT
television receiver would methodically
scan the face of the image dissector now
as we all know opposites attract and
likes repel electrons really don't like
to hang out together what happens when
the electron beam encounters an area of
the image dissector where bright light
is hitting the surface while the cesium
oxide coating is itself producing
electrons so the electron beam would
bounce back at areas where liked was
already present ordinarily most of the
beam would just be absorbed by the oxide
coating or even the tubes glass but any
electrons sent by the gun that ran into
a spot already filled with electrons
emitted from the cesium oxide would be
reflected back into the tube the image
dissector contained a detector of sorts
that would collect these reflected
electrons by amplifying the output of
the detector a signal could be produced
which corresponded to the exact image
brightness of wherever the beam happened
to be pointing on the surface of the
image dissector deflect the beam in a
raster pattern using electromagnetic
field from a deflection yoke and you can
scan the whole face of the dye sector
and generate a signal from the entire
image here's a more practical
demonstration of what's going on this
poster board represents the target of
the scanning electron beam the image
we're looking to capture is a simple
white circle a lens is focusing that
circle onto the face of the image
dissector the circle of light which
moves us all by the way will cause the
cesium oxide coating to emit electrons
inside the tube wherever the light
touches well represent electrons in red
therefore the circle will be filled with
red electrons it should be noted here
that the resemblance to the Japanese
flag was entirely accidental it took me
filling in over 90% of this to realize
that's the flag of Japan anyway the
electron gun sits
the caesium oxide and it emits a string
of yarn I mean an electron beam
deflector magnets Bend the electron beam
and we'll start scanning the image for
the first few lines nothing
extraordinary occurs as the electrons
are just absorbed by the target but once
the beam reaches the circle it gets
deflected back because electrons are
already there in other words where the
light touches the electrons must never
go there these deflected electrons get
picked up by a collector electrode
inside the tomb and by monitoring the
output from this electrode you get a
signal which varies in intensity in
proportion to the brightness of the spot
the beam is currently scanning so
reverse the process here's a television
receiver its electron beam is following
along the same path as the one in the
image dissector so if the scanning beam
is aimed at one spot the electron beam
in the television set will be pointed at
the same spot whenever the dissector
detects light from the circle the signal
it produces will cause the television
receiver to spit electrons out from its
own electron gun this will make the
phosphors inside the tube glow in the
same places that the dissector detected
light and at the same relative intensity
after the scanning is complete the
television will have drawn that circle
do that really really fast and over and
over again and you've got yourself some
mighty fine television if you're
confused and I wouldn't blame you if you
are it might be helpful to check out my
previous video on how analog television
works that video discusses the raster
pattern how the television synchronizes
the image coherently via triggers built
into the signal and more in greater
detail hopefully you'll be able to see
that the television camera tube is
essentially the same thing as the
cathode ray tube in a television set but
with the electron being used as a way to
detect the presence of light rather than
to reproduce it you can find a link to
the video down below or hang around
until the end screen Farnsworth's image
dissector was a big deal but it kind of
sucked because the beam has to move
across the face of the dissector so
quickly in order to produce an image it
has only the tiniest fraction of a
second to actually encounter an electron
on the surface and be deflected back the
caesium oxide coating wasn't super great
at producing electrons from light so
television cameras that used
Farnsworth's image dissector needed an
insane amount of light in order to work
this meant studio lighting was absurdly
bright
and hot and it generally presented
unfortunate limitations a much more
practical device for producing
television signals was the Icona scope
here comes another person into the fold
Vladimir Zworykin filed patents for a
television system in 1927 and 1925 if
you've been paying attention you'll have
noticed that these years predate
Farnsworth patent application I told you
this was complicated in 1923
vory can presented his idea to HP davis
the general manager of westinghouse
where he worked and in 1925 he
demonstrated the first prototype however
it barely worked and Davis wasn't
impressed
so unfazed was davis that he told Sorkin
to work on something useful
his very keen would later work for RCA
the Icona scoop functioned essentially
the same as the image dissector but
there was one key difference and Vorian
wasn't the one who discovered the
principle that would solve the problem
that was Hungarian engineer Col Monty
Hani there's way too many people here
anyway the big deal with the Icona scope
was that it didn't rely solely on
electrons emitted from the cesium oxide
rather it used a sheet of mica which had
tiny silver particles coated with her
friends cesium oxide on one side and a
thin film of plain old silver on the
other the separation of these two sheets
provided by the mica essentially turned
the thing into a giant capacitor capable
of storing electrons when operating the
Icona scope would first send a steady
sweep of electrons across the whole
target this would provide a uniform
charge throughout the night to sheet
light reflected from subjects in the
studio and subsequently focused through
a lens on to the target would cause the
cesium oxide to emit electrons again in
the spot set with light creating an
electron copy of the image and this
would cause the charge stored between
the layers to decay more rapidly than it
would if no light were hitting it the
next time the target is scanned areas
that weren't hit with light will still
have electrons in them which will resist
the beams efforts to try and add more
this extra beam energy is reflected back
and picked up by the detector ring areas
that weren't hit with light would
quickly lose their electrons and the
beams energy would instead be used to
replenish these lost electrons the icon
ESCO produced an inverted signal as dark
areas reflected the beam strongly and
bright areas didn't reflect it much at
all but it was
much much much more sensitive than
Farnsworth's image dissector because it
could store electrons in the mica sheet
and thus greatly increased the
likelihood that the electron beam would
actually be deflected back to the
detector one tricky bit about the Icona
scope was that the light it was
detecting and the electron beam had to
hit the mica sheet from the same side
this is why the tube is such a weird
shape the electron gun can't be in the
line of sight of the target so it's
tucked below the target screen at an
angle in a working camera it's actually
in front resting below the lens
electronics in the camera would adjust
its scanning sweeps as it went to
compensate for the keystone shape it
would naturally produce if the beam was
projected as a simple square at an
upwards angle a side effect of the way
the icon is cook works is an image that
can never truly be black electrons will
decay from the mica screen without any
light hitting it at all light simply
accelerates this decay the detector ring
would pick up these rogue electrons and
it would transmit as an entirely gray
screen there needed to be bright areas
of the picture to pull down the average
emission of the mica screen and make the
other areas appear black in other words
high contrast scenery was required
lighting conditions would have to be
accounted forward to keep the averaging
effect of the Econo scope from producing
odd-looking images because this episode
is the circus of who did what let's drop
one more name the Icona scope design was
in mentally improved by accident in 1931
when Sanford Essig left one of the mica
plates in the oven too long this broke
up the silver layer into tiny globules
which was responsible for increasing the
resolution the Icona scope could detect
immensely therefore a sharper image was
produced so don't forget about him
although the Icona scope was a great
improvement over Farnsworth's image
dissector it still wasn't that great the
images were noisy of poor resolution and
it still required a lot of light though
far less than the original dissector did
RCA would develop the image orthicon
tube in the 1940s and this much more
sensitive device would be used into the
60s the image orthicon tube combined
principles of the Econo scope image
dissector and the original orthicon tube
the orthicon tube along with the
european cps a Metron tube contained
deflector plates that when calibrated
correctly would reduce the velocity of
the scanning electrons
from the electron gun to almost zero as
they approach the target this was
immensely helpful because without these
deflectors electrons could still bounce
back into the detector ring without
photo electrons being present this
created for a noisy picture slowing the
electrons down before they hit the
target meant almost no rogue electrons
would have enough gusto to make it back
to the detector only those scanning
electrons that actually encountered
another electron at the target would
make their way back as the actual
repelling force imparted by its
photoelectric neighbor would help to
push it backwards this greatly reduced
the grainy image noise associated with
ordinary tubes in addition to the
electron slow down easing the image
orthicon tube used a neat physics trick
to amplify the effect of the photo
electrons and make the whole thing more
sensitive in an image orthicon tube the
surface the light falls on to make the
image called the photo cathode and the
surface the electron beam scans to make
the signal called the target are
separated by a fairly great distance the
photo cathode is negatively charged
meaning electrons near it will want to
fly away from it and in front of the
scanning target is a wire mesh with a
slight positive charge used to attract
the photo electrons
this causes the photoelectrons emitted
from the photo cathode to be accelerated
towards the scanning target the
separation of photo cathode and target
causes a dramatic increase in speed of
the photo electrons which results in a
multiplication of the electrons
generated from the image this happens
because when an individual electron
slams into the target at high speed it
causes a splash forcing many more
electrons out of the target this is
called secondary emission and a wire
mesh behind the target with a slight
positive charge traps these extra
electrons this phenomenon is used to
greatly increase the tubes sensitivity
you see the extra electrons produced
when the first photo electron hit the
target came from within the target
itself essentially the high speed of the
photo electron knocks out a whole bunch
of other electrons when it hits the
target this causes a net loss of
electrons in the area of impact giving
that area of the scanning target a
slight positive charge when the scanning
beam from the electron gun runs over
this area the electrons and emits are
first used to refill those lost from the
secondary emission event the result is
that bright areas of the picture used
the beams energy to recharge the target
and no
electrons are reflected back and
detected dark areas of the image don't
displace electrons and the targets of
the beam is reflected back as electrons
are already there and a strong signal is
produced to be in the diodes and
electron multiplier at the base of the
tube the image orthicon tube was a big
deal for many reasons not the least of
which was that cameras could be much
smaller and less awkward as the scanning
portion of the tube was no longer in
front of the imaging target but it was
also sensitive enough to capture scenes
lit by candlelight and as logarithmic
light sensitivity matches that of the
human eye which made images produced
from these tubes appear more natural a
fun little fact immortalized by
Wikipedia regarding the image orthicon
tube is that it's directly responsible
for the name of the award given by the
Academy of Television Arts and Sciences
image orthicon tubes were often referred
to informally as Emmys the president of
the Academy at the time
Harry lub key wanted to name the award
after the Emmy
but since the statuette is female the
more feminine Emmy was chosen the
inverted signals of the image orthicon
and Icona scope meaning bright areas
produced little to no signal and dark
areas produce a strong signal wasn't a
problem as this is how television
broadcasts were transmitted anyway it
was up to your TV set to flip those
values around yeah that was complicated
and I didn't even mention kenjiro taka
yanagi's 1926 demonstration in Japan of
a CRT based television system sadly he
doesn't get much credit because his
camera was still mechanical using a
nipped off disc there I said it
nipped off or should it be nipkow as
some have suggested I don't know maybe
you should argue about it in the
comments there are so many dots to
connect here that I'm not going to claim
I got it all correct for one thing it's
hard to pin down how developments in
Europe affected those in the US and vice
versa particularly due to the patent
dispute between Farnsworth of Oregon
which made new developments dance around
their respective technological claims
this is a large part of why I didn't go
into much detail on European tubes and
systems and all the names given to all
the tubes is very confusing for creating
a research timeline in my head I'm
welcome to all comments that may set
record straight so leave them below this
video is long enough so I'll be ending
in here stay tuned as in the next video
we'll be looking at the next big thing
in TV call
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well
and we'll change the arm again