Development of ultrahigh-sensitivity HDTV camera for deep

Development of ultrahigh-sensitivity HDTV camera for deep
Development of ultrahigh-sensitivity HDTV
camera for deep-sea exploration
housing camera
O
ur research on ultrahighsensitivity image pick-up
tubes is intended for
HDTV cameras that is usedfor
reporting breaking news at night
and producing nature and
science programs. On the basis of
this research, we have developed
an ultrahigh-sensitivity HDTV
camera for 3000-m-class deep-sea
exploration, in cooperation with
the Japan Marine Science and
Technology Center (JAMSTEC).
This camera is the first of its kind.
Deep underwater, sufficient
brightness is often unobtainable,
even if artificial illumination is
used because the light intensity
greatly decreases the deeper one
goes. If a normal-sensitivity
camera is used under such
conditions, it will not yield an
adequate depth of field since the
camera would have to have a
low F-number lens. Therefore,
clear images cannot be produced.
In contrast, the New Super-HARP
image pickup tube we developed
does not suffer from this problem.
We employed it in the HDTV
camera for deep-sea exploration.
Our HARP pickup tube makes use
of the "avalanche multiplication
phenomenon"
in
its
photoconductive film. The thicker
the HARP film, the longer the
avalanche multiplication process,
which results in a higher
multiplication factor. We
achieved a factor of 200, which is
about four times higher than that
of conventional 8- m-thick
HARP film, by almost doubling
the thickness to 15 m, and
improved the heat resistance of
the film by doping it with
impurities.
Our camera for deep-sea
exploration is housed in a
compact housing capable of
18
prism
pickup tube
housing
circuit plates
zooming lens
Figure 2: Ultrahigh-sensitivity HDTV camera
for deep-sea exploration
camera
Figure 1: Special prism system
withstanding the high pressure
of the deep-sea environment.
This compact housing also
enables us to pan and tilt the
camera widely. Thus, the
camera itself needs to be
compact enough to fit in such a
housing. As shown in Figure 1,
we developed a special prism
system that reduces the
dimensions of the camera
including the pickup tubes. The
prism divides incident light into
blue, green and red beams, and
reflects them 180 degrees. This
enables us to arrange pickup
tubes in parallel in the space
around the zoom lens, resulting
in a compact camera.
Figure 2 shows the completed
camera. Its sensitivity of 2 Lux
F1.8 is 30 times higher than that
of an HDTV CCD camera, and it
measures just 19 cm in diameter
and 45 cm in length, including
the zoom lens.
On November 15 and 16, the
world's first HDTV live relay
broadcast from the deep sea was
conducted from the seabed at a
1200-m depth off the coast of
Hatsushima Island in Sagami
Bay. We mounted the camera on
JAMSTEC's
3000-m-class
unmanned submersible, called
"Hyper Dolphin" (Figure 3), and
shot underwater scenes with it.
Figure 3: Hyper Dolphin
Figure 4: Relayed image (fish and rocks)
The HDTV video shot by Hyper
Dolphin was sent to the control
room in the mother ship via an
optical cable. An NHK outside
broadcasting van containing
equipment to automatically track
a communications satellite was
loaded onto the mother ship's
deck. It relayed the images from
the deep-sea to the studio. The
result was a broadcast of
excellent HDTV images of the
clams, fish, and crabs that
inhabit the deep sea. As you can
see in Figure 4, we obtained wellfocused HDTV images, even of
nooks and corners, by using the
camera's high F-number lens and
its ultrahigh sensitivity.
* This camera belongs to JAMSTEC.
Broadcast Technology no.14, Spring 2003
C
NHK STRL
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