Talking Stone Film

Film Reviews & Headlines


In my last video I looked railguns, now
whilst I was reviewing the footage I started wondering how they filmed the
projectiles in flight. These are not the typical sort of high-speed camera shots
where you see a bullet hitting a target for example, these are tracking the
projectile from the barrel down the firing range. From the footage it looks
like the camera is panning around and following the projectile but that would
be impossible, the tank round is traveling at over 1,500 meters per
second and would normally look like this. For all of you out there who said it’s
done with mirrors then you are absolutely correct.
It works by having a computer-controlled high-speed rotating mirror in line of
sight of a high-speed camera. The speed of the rotation of a mirror matches that
of the object being followed so the faster the object is traveling like a
railgun projectile the faster the mirror would turn to keep up with it. Using this
method the object can be kept in the field of view for a hundred meters or so
or about ninety degrees of the mirrors movement. In this example the tracker 2
from specialized imaging you can see the mirror and to its left where the camera
is. Because the mirror is computer-controlled it can be programmed
to follow objects that accelerate even linearly or non linearly. Now rotating
mirrors aren’t new in fact they were some of the first high-speed cameras and
are still some of the fastest in the world capable of up to 25 million frames
per second and were used to record atom bomb blasts. During the Manhattan Project to develop the first atomic bomb they required cameras that could record the
first few microseconds of explosion. In order to create a nuclear chain reaction
and achieve critical mass a baseball-sized piece of plutonium had to
be compressed to about half its size. This was achieved by using an array of
focused high explosive lenses surrounding the plutonium core. In order
to make it work effectively the explosives 32 of them in all had to be
triggered within one microsecond, if any were delayed then the compression
of the core would be unequal and the reaction would even be much less or may
not even happen at all. Using a super high-speed camera it will
be possible to see how effective the explosive lenses had been just a few
microseconds after detonation. At the time the fastest cameras were Fastax
cine cameras and could achieve around 10,000 frames per second or one frame
per hundred microseconds, this still wasn’t fast enough though. The first
high-speed rotating mirror camera was the Marley, invented by of a British
physicist William Gregory Marley, the Marley camera used a rotating mirror an
array of lenses inside a curved housing each focused onto a single piece of film
around the edge of the case. This could record a sequence of up to 50 images
onto 35 millimeter film at a 100,000 frames per second. But by the
time of a Trinity test it was outdated and too slow to record the ultra quick
reaction in the plutonium core. Head of the photography unit Julian Mack said that
the fixed short focus and low quality of the lenses would probably have made the
Marley camera pictures useless. He helped develop the Mack Streak camera
which had a 10 million frames per second limit, thats one frame every hundred
nanoseconds. By the 1950s Harold Edgerton had developed the Rapatronic camera
the name coming from Rapid Action Electronic this used a magneto-optic
shutter which allowed it to have an exposure time as short as 10 nanoseconds
thats ten billionths of a second. This was first used with a hydrogen bomb test of
Eniwetok Atoll in 1952. However they only took one image so to
see the first few microseconds of a nuclear detonation up to 10 were used
in sequence with an average exposure time of three microseconds. The images
were then played back and blended together to give the impression of a
film. For the British nuclear tests the Atomic Weapons Research
Establishment created for C4, a huge rotating mirror camera weighing in at
around 2,000 kilograms and was the fastest in
the world at the time. This could record up to 7 million frames per second who
have a mirror rotating up to 300,000 revolutions per minute and recorded the
first British atom bomb test on the 3rd of October 1952. The rotating mirror
cameras are still in use today but now they use highly sensitive CCDs
to replace the filmstrip. The Brandaris 128 and Cordin model 510 have 128 CCD’s and a gas driven turbine mirror driven by helium to achieve up to 25
million frames per second at a resolution of 500 x 292 pixels for the
brand iris and 616 x 920 pixels of recording. At 25 million
frames per second the mirror itself is running at 1.2 million
revolutions per minute that’s 20,000 revolutions per second so fast of the
atmosphere inside the camera is 98% helium to reduce for friction and the
pressure waves that would occur in normal air. And so onto something I think
you may find rather interesting. It’s not the fastest camera in the world but this
one is or it was at the time in 2013 the fastest real-time tracker of a moving
object and was developed by the Ishikawa Oku Lab at the University of Tokyo. Here
it is tracking a ping pong ball and keeping it in the center of a frame all
times both during a game and when it is being spun around on a piece of string.
It does this by moving two mirrors in front of the camera one for the X
movement and Yvon for the Y movement it then uses software similar to face
tracking software to provide feedback to control the mirrors with a response time
of just one millisecond. It can also be used to control a projector and in this
scene it’s projecting an image onto the ping-pong ball whilst it’s been bounced
on the bat, you can see the little face change on the ball at the top of its
travel. So anyways I hope you enjoyed this look at some of the equipment behind some of the most amazing footage recorded to date
these aren’t the fastest cameras in the world now but it’s still amazing to
think what can be achieved by mechanical means. So as always thanks for watching
and don’t forget we also have the curious droid Facebook page and I would
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