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Many physical processes evolve on timescales shorter than the human eye
can resolve. Effectively, this means the details of how the process
changes with time are lost in a blur. High speed photography, or HSP,
is simply photography with extremely short exposure times, yet it can provide
a permanent record of the evolution of a process, with detail unattainable
with the human eye.
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Recording the complete evolution of a process on film requires a sequence of
photographs. The motion-picture method involves taking many photographs during
a single "trial" of the process. Essentially, this is a professional pursuit,
requiring very sofisticated and expensive equiptment.
Obtaining a single photograph while the process is evolving is considerably
less complex, and quite inexpensive. With this snap-shot method of HSP,
process evolution can be observed by obtaining many snap-shots at different
stages in the evolution, though each snap-shot is made on a new "trial" of
the process.
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To compare the motion-picture and snap shot methods of HSP, consider a drop of
water splashing on a flat surface. To record the evolution of the splash, the
motion-picture method would take a photo every ten-thousanth of a second while
a single drop was first falling, then splashing. For every second that the drop
was filmed, 10,000 images would be recorded.
The snap-shot method would take a single shot, say 1 second after the drop
began to fall, taking an image of the drop, just before it hit the surface.
Another drop would then be spilt, and a photograph taken 1.1 seconds later,
recording a picture of the drop as it strikes the surface. The process of
spilling a drop and taking a snap-shot is repeated, the photograph being taken
0.1 seconds later each time. For 1 second of evolution of the splash, the
snap-shot method would take 10 photographs, each at a different stage in the
splash evolution, though each photo is of a different drop. The downside of
the snap-shot method is simple - no two drops will have precisely the same
splash. On the other hand, a single photograph can provide both a facsinating,
and visually spectacular image, and all within the reach of the enthusiust.
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The field of high speed photography was pioneered by Eadweard Muybridge in
1872, in an attempt to prove that a galloping horse has all four hooves off the
ground at some point in its stride. Almost 50 years later, Harold E. Edgerton
developed a strobe flash, and pushed the field forward as a tool for science.
Almost all of the published photographs of high speed events were produced by
Doc Edgerton.