From: Doug White <gwhite@ll.mit.edu>
Subject: Re: [Photography (?!?)] Still pictures of bullets
Organization: MIT Lincoln Laboratory

I've been on vacation, so I missed the beginnings of this thread.  I was
a lab/teaching assistant in Doc Edgerton's High Speed Photography course
for a year, and I've taken dozens of bullet photos.  Other than a gun and
a bullet trap, you need 2 special gadgets:

1) A crystal microphone with the diaphram removed.  This makes it very
insensitive, so it will only pick up the strong shock wave from a passing
bullet.  This is used to trigger the strobe.  To get the bullet in the
frame, you just slide the microphone along the bullets path until the timing
is right.

2) A special high speed strobe.  Normal Xenon strobes are very bright, but
the flash duration is way too long for bullets.  Although not nearly as
efficient, the strobe we used was an air spark in a special quartz tube.
The capacitor bank ran at about 4KV (if my memory serves me).  It was
a commercial unit built by EG&G (Edgerton's company), so I don't know all
of the internal details.  There was a trigger electrode that fired the main
spark, but I don't know what was used to connect the crystal mic to the
trigger discharge.  This is all from memory, but I recall that the discharge
time was under a microsecond.  The spark tube need to be cleaned periodically,
and I was one of the few T.A.'s who managed to do it without accidentally
getting across the capacitor bank.  They still pack quite a kick even after
they've been recently discharged.

You could actually do a lot of the setup with your eyes.  You turn off the
lights, let your eyes adjust, and then fire the gun while looking in the
general area where the bullet should be.  With a white piece of paper just
behind the bullets path, you could usually spot it with your eyes.  Then
you adjusted the microphone, camera, and target (usually a playing card)
so that everything lined up.

We had a lot of students trying to come up with something more original
than cutting a card in half.  We let them shoot anything that wasn't hard
enough to deflect the bullet; smurfs, candy bars etc.  The one problem
area was fruit.  Edgerton's famous photo of an apple being hit with a
30-06 doesn't mention the fact that the entire lab was full of apple sauce
a millisecond after the photo was taken.  On really hot humid days you could
smell it YEARS after the fact.  We had one guy shoot a banana lengthwise,
but we made him build a banana trap first.

Doug White
MIT Lincoln Laboratory