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Re: High speed arc photos: rotating mirror vs streak camera
Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
At 09:48 PM 9/19/2006, Tesla list wrote:
Original poster: "Scott Hanson" <huil888@xxxxxxxxxxxx>
Just to stimulate further discussion & experimentation, there are at
least two techniques that can be used to separate and record the
multiple discharges that make up a tesla coil streamer.
In the first technique, the moving image is swept across a fixed
detector. This can be accomplished by using a rotating mirror, etc,
to sweep the image across photographic film or a CCD detector. This
is the technique being used by Peter and Terry.
In the second technique, a fixed image is projected onto a moving
detector, the "detector" usually being photographic film. This is
the classic technique used in some types of high speed motion
picture cameras, where a length of film is "accordian-folded" into a
canister, then rapidly accellerated to a high linear speed just
milliseconds before the "event" is triggered.
Do a web search for "streak camera" and you'll find info on many
different implementations of streak cameras, some specifically for
capturing high-speed events. Some clever modifications have been
made to motor-drive 35mm cameras to convert them to streak-camera
function. A 35mm camera will allow the use of specialized high-speed
(high-sensitivity) films, but of course requires processing before
the results can be viewed.
There are also schemes where the film is on a drum that is spun.
If you run the math for reasonable frame sizes and high frame rates
(1 Mfps), you'll find that you need to spin that mirror pretty darn
fast (as in, using a diegrinder air motor fast).
Very high speed cameras these days use electronic shutters and image
intensifiers. The standard image intensifier can also serve as a
shutter by driving the bias appropriately. Surely an ambitious TCer
would have no problem making short HV pulses, eh?
There are also such things as Pockels and Kerr cells (the latter is
faster), which are electrically driven. One could set up a whole
series of inexpensive, but slow, cameras, with fast shutters in front
of them that are triggered in sequence by some sort of timing
apparatus. An updated version of Muybridge, if you will.