"The exposures are at 1/100,000,000ths of a second"

"Kennedy McEwen" wrote in message
...
In article , William Graham
writes


So all I guess I need to know is how to get a 1/millionth second
shutter.....I don't know how to rotate a polarizer that fast, and I don't
understand the other faraday reference.....I know that I used to use a
Tectronics capture scope that couldn't even blank off the erase pulse,
which
used to destroy my vision in a darkened room every few seconds.....I don't
know why they didn't blank that off with a standard mechanical shutter,
much
less a millionth second electronic one.....

The Kerr cell is only one way of achieving this sort of shutter time. I
posted a link to a gated intensifier camera the other day with a 10nS gate
period (which is the electronic equivalent of the shutter).

http://www.linuxdevices.com/articles/AT2171151224.html

I worked with a similar system based on an intensified isocon camera for
low light imaging back in the early 80's, although that had been in
service with the RAF for at least a decade by then.

There are equivalent solid state devices available these days, some of
which are used for laser gated imaging, for example in cost effective
undersea surveillance from an aircraft. In such systems the rapid shutter
speed, coupled to a pulsed laser illumination source, permits the camera
shutter to be closed when the laser pulse is reflected by the sea surface,
but opened when the reflection from the sea bed returns. This effectively
eliminated the reflection from the ocean surface from the images,
permitting clear images of the sea bed to be obtained. Obviously, since
the sea water rapidly attenuates the laser light there are limits as to
how deep you can image, hence the need for high sensitivity as well as
fast shutter speed.

Yes. that would be an excellent use of a super fast shutter. It is similar
to the problem of the power pulse in a radar set burning out the sensitive
receiver that must be attached to the same waveguide to capture the much
lower intensity received pulse. Basically this was accomplished by "shorting
out" the waveguide path to the receiver, using the power pulse itself to do
the shorting......

"Dave Martindale" wrote in message
...
"William Graham" writes:

So all I guess I need to know is how to get a 1/millionth second
shutter.....I don't know how to rotate a polarizer that fast, and I don't
understand the other faraday reference.....

You need a substance that changes the amount it rotates polarized light
depending on the voltage applied. Liquid crystals work that way, but
they're too slow for this use. But there are other faster
technologies.

I know that I used to use a
Tectronics capture scope that couldn't even blank off the erase pulse,
which
used to destroy my vision in a darkened room every few seconds.....I don't
know why they didn't blank that off with a standard mechanical shutter,
much
less a millionth second electronic one.....

And how would you go about that? The erase is done by flooding the
screen with electrons for a significant fraction of a second, to
equalize the charge on the storage grid behind the screen. The only way
to block that is have a shutter between your eye and the screen - which
means a full-screen-sized shutter (impractical if mechanical, expensive
if electronic), or forcing you to look through a small hole that can
have a small shutter protecting it.

Anyway, aren't you glad that these have mostly been replaced by digital
storage? Now the image doesn't degrade no matter how long you look at
it, and you don't get fainter images at faster writing speeds, and you
can even print the waveform or save it on your PC, instead of having to
photograph it on film before it decayed. (See, there's a camera in this
posting after all).

Dave

Yes. (I am glad) But even at the time I was doing this (some thirty years
ago) they had all the time in the world to shutter off that erase pulse. I
could have done it with a motor driven window shade..:^) I did get rather
good at simply closing my eyes during the erase time.......

In article , William Graham
writes

It is similar
to the problem of the power pulse in a radar set burning out the sensitive
receiver that must be attached to the same waveguide to capture the much
lower intensity received pulse.

A similar effect to the laser back-scatter from close range atmospheric
suspensions swamping out the much lower intensity signals from the
scene. This is quite common on laser illuminated systems and the gated
sensor is a neat solution.

There is a classic example of this shown he
http://www.obzerv.com/video/Snowfall_large.html

In this case the image is totally obscured by reflections from the close
range falling snow, in fact the snow is falling so heavily that it would
obscure the scene in any case. However, by extending the delay between
the laser firing and the sensor gate (shutter) opening, the sensor can
suddenly see right through the falling snow without significant loss of
contrast.

There were times when I was shooting in smoke filled rooms years ago
when this technology would have been most welcome. Fortunately, that
particular form of pollution has diminished - and in some places become
illegal - so it is less of an issue for photographers these days.

Basically this was accomplished by "shorting
out" the waveguide path to the receiver, using the power pulse itself to do
the shorting......

Actually, in the solid state devices I referred to, that is almost
exactly what is done - the storage well is effectively shorted out until
the start of the gate. All of which goes to show that there is nothing
new. ;-) Controlling the back edge of the gate is a lot trickier
though. ;-)
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)

"Dave Martindale" wrote:
"William Graham" writes:

So all I guess I need to know is how to get a 1/millionth second
shutter.....I don't know how to rotate a polarizer that fast, and I don't
understand the other faraday reference.....

You need a substance that changes the amount it rotates polarized light
depending on the voltage applied. Liquid crystals work that way, but
they're too slow for this use. But there are other faster
technologies.

If you could spin a disk with a slot at the edge that was 1/1000 of the
circumference at 1000 rpm (and sync a slower (slightly under 1/500th)
secondary shutter to it), you'd be home free.

David J. Littleboy
Tokyo, Japan

In article , David J. Littleboy
writes
"Dave Martindale" wrote:
"William Graham" writes:

So all I guess I need to know is how to get a 1/millionth second
shutter.....I don't know how to rotate a polarizer that fast, and I don't
understand the other faraday reference.....

You need a substance that changes the amount it rotates polarized light
depending on the voltage applied. Liquid crystals work that way, but
they're too slow for this use. But there are other faster
technologies.

If you could spin a disk with a slot at the edge that was 1/1000 of the
circumference at 1000 rpm (and sync a slower (slightly under 1/500th)
secondary shutter to it), you'd be home free.

I think you may have meant to say 1000 rps (i.e. 60,000 rpm) there - a
slightly more challenging proposition.

David
--
David Littlewood

"Kennedy McEwen" wrote in message
...
In article , William Graham
writes

It is similar
to the problem of the power pulse in a radar set burning out the sensitive
receiver that must be attached to the same waveguide to capture the much
lower intensity received pulse.

A similar effect to the laser back-scatter from close range atmospheric
suspensions swamping out the much lower intensity signals from the scene.
This is quite common on laser illuminated systems and the gated sensor is
a neat solution.

There is a classic example of this shown he
http://www.obzerv.com/video/Snowfall_large.html

In this case the image is totally obscured by reflections from the close
range falling snow, in fact the snow is falling so heavily that it would
obscure the scene in any case. However, by extending the delay between
the laser firing and the sensor gate (shutter) opening, the sensor can
suddenly see right through the falling snow without significant loss of
contrast.

There were times when I was shooting in smoke filled rooms years ago when
this technology would have been most welcome. Fortunately, that
particular form of pollution has diminished - and in some places become
illegal - so it is less of an issue for photographers these days.

Basically this was accomplished by "shorting
out" the waveguide path to the receiver, using the power pulse itself to
do
the shorting......

Actually, in the solid state devices I referred to, that is almost exactly
what is done - the storage well is effectively shorted out until the start
of the gate. All of which goes to show that there is nothing new. ;-)
Controlling the back edge of the gate is a lot trickier though. ;-)

With the radar, we called this, "sea return". the close in ocean waves would
block the receiver with returned radar pulses.....We gated this off by
reducing the receiver sensitivity for a short (variable) time period right
after the transmitted pulse.....We were usually interested in targets over
100 yards or so from the ship, so this introduced no problems.....

"David J. Littleboy" wrote in message
...
"Dave Martindale" wrote:
"William Graham" writes:

So all I guess I need to know is how to get a 1/millionth second
shutter.....I don't know how to rotate a polarizer that fast, and I don't
understand the other faraday reference.....

You need a substance that changes the amount it rotates polarized light
depending on the voltage applied. Liquid crystals work that way, but
they're too slow for this use. But there are other faster
technologies.

If you could spin a disk with a slot at the edge that was 1/1000 of the
circumference at 1000 rpm (and sync a slower (slightly under 1/500th)
secondary shutter to it), you'd be home free.

Yes, but you would have to synch it to your subject....With the atomic
blast, the military would have to let you trigger the blast to your shutter,
otherwise, with my luck, you can bet the bomb would detonate right after the
slit whipped by my lens, and by the time it came around again, it would be
all over but the mopping up....:^)

"David J. Littleboy" writes:

"Dave Martindale" wrote:
"William Graham" writes:

So all I guess I need to know is how to get a 1/millionth second
shutter.....I don't know how to rotate a polarizer that fast, and I don't
understand the other faraday reference.....

You need a substance that changes the amount it rotates polarized light
depending on the voltage applied. Liquid crystals work that way, but
they're too slow for this use. But there are other faster
technologies.

If you could spin a disk with a slot at the edge that was 1/1000 of the
circumference at 1000 rpm (and sync a slower (slightly under 1/500th)
secondary shutter to it), you'd be home free.

1000 rpm won't be quite enough. 60000 rpm would.

--
Måns Rullgård

"William Graham" wrote in message
...

"Kennedy McEwen" wrote in message
...
In article , William Graham
writes


SNIP

There are equivalent solid state devices available these days, some of
which are used for laser gated imaging, for example in cost effective
undersea surveillance from an aircraft. In such systems the rapid
shutter speed, coupled to a pulsed laser illumination source, permits the
camera shutter to be closed when the laser pulse is reflected by the sea
surface, but opened when the reflection from the sea bed returns. This
effectively eliminated the reflection from the ocean surface from the
images, permitting clear images of the sea bed to be obtained. Obviously,
since the sea water rapidly attenuates the laser light there are limits
as to how deep you can image, hence the need for high sensitivity as well
as fast shutter speed.

Yes. that would be an excellent use of a super fast shutter. It is similar
to the problem of the power pulse in a radar set burning out the sensitive
receiver that must be attached to the same waveguide to capture the much
lower intensity received pulse. Basically this was accomplished by
"shorting out" the waveguide path to the receiver, using the power pulse
itself to do the shorting......
Not surprisingly there is an analogy in nature.
Bats use echo-location, and to avoid deafening themselves with their own
chirp, they have a tiny muscle that locks the inner-ear bones.
Completely OT, but I thought I'd share ;-)

Deep.

"Måns Rullgård" wrote in message
...
"David J. Littleboy" writes:

"Dave Martindale" wrote:
"William Graham" writes:

So all I guess I need to know is how to get a 1/millionth second
shutter.....I don't know how to rotate a polarizer that fast, and I
don't
understand the other faraday reference.....

You need a substance that changes the amount it rotates polarized light
depending on the voltage applied. Liquid crystals work that way, but
they're too slow for this use. But there are other faster
technologies.

If you could spin a disk with a slot at the edge that was 1/1000 of the
circumference at 1000 rpm (and sync a slower (slightly under 1/500th)
secondary shutter to it), you'd be home free.

1000 rpm won't be quite enough. 60000 rpm would.

Why not? 1/1000 of 1/1000 used to be 1 millionth...

David J. Littleboy
Tokyo, Japan