High-speed photography with a digital camera


(click on any of the images on this page to see a much larger version)

High-speed photography (also called "stop-motion" photography) is defined as taking "fast" pictures - in other words, pictures with very short exposure times. Typical exposure times are on the order of a thousandth to a millionth of a second. Since most cameras do not have shutters which are that fast, high-speed photography uses a flash in place of a shutter. In other words, in "normal" photography, the camera's shutter is used to start and stop of the exposure of the film (or image sensor, for digital cameras). In high-speed photography, an electronic flash is used to start and stop of the exposure. (The exposure continues for as long as the flash continues to emit light).

It is relatively easy to take high-speed photographs. All you need is a sound-triggered flash (with variable delay), a camera that has a "bulb" setting or that can take two-second time exposures, and a perfectly dark room - say a garage that has had all of the windows covered with black plastic. The key piece of equipment is the sound-triggerd flash with variable delay. Basically, this is an electronic device which detects a sharp noise (like the firing of a BB gun or the popping of a balloon), waits for a pre-determined amount of time, and then fires the flash, which illuminates the scene and exposes the film in the camera.

Let's say that we are going to take a typical high-speed photograph - one of a light bulb shattering when it's shot with a BB gun (see the picture at the top of the page). If you dial a short delay into the flash, then you might get a picture of the BB and the light bulb just before the BB hits the bulb. With a slightly longer delay, you might get a picture with the BB inside the light bulb. With an even longer delay, you might get a picture with the BB on the other side of the light bulb and the light bulb beginning to break up. The process of taking this picture of the shattering light bulb involves seven basic steps:
  1. The camera is placed on a tripod and pointed at and focused on the light bulb.
  2. The BB gun is clamped into a holder and aimed at the light bulb.
  3. The lights are turned off / the room is made completely dark.
  4. The shutter of the camera is opened, but no light gets into the camera because the room is completely dark.
  5. The BB gun is fired. The sound of the BB gun firing triggers the variable-delay circuit, and after the delay time is up, the flash is fired, illuminating the scene for about a thousandth of a second, which exposes the film in the camera.
  6. The shutter of the camera is closed.
  7. The lights are turned back on, and if you used a digital camera, you see how the picture turned out.
If your camera does not have a "bulb" setting, but does allow 2 second (or 4 second) time exposures, in step 4, you start the exposure, and then quickly proceed to step 5, before the shutter closes. After step 5, you wait for a few seconds to make sure that the camera shutter has closed, and then you proceed to step 7.

The trick is getting the delay set right. If the delay is too short, you get a picture of an un-broken light bulb because the BB hasn't arrived from the gun yet. If the delay is too long, you get a picture of a bunch of glass shards sitting on the floor. The best pictures generally result from firing the flash just after the BB hits the light bulb. A simple (and inexpensive) way to get the delay right is to shoot saltine crackers. This lets you waste inexpensive saltines while you adjust the delay (and the exposure - camera aperture, etc.) instead of wasting expensive light bulbs. Saltines are also nice because they don't scatter sharp glass shards all over the place.

In picture #1 (below), the BB (which is moving right-to-left in all of the pictures) has not arrived at the cracker yet. (The piece of broken cracker on the left is from a previous shot.) The cracker is sitting on top of a can and is held upright by being grabbed at the corner by a pair of needle-noze pliers which have a rubber band wrapped around the handles to provide pressure. Picture #2 shows the BB just smashing into the center of the cracker. Notice the bits of dust flying off of the cracker around the edges. Picture #3 shows the cracker soon after the BB has punched through it. In picture #4, the BB is long gone. Only the cloud of cracker dust remains.

Picture #1
Picture #2
Picture #3
Picture #4

The cloud of cracker dust makes it very easy to tell if the BB has passed through the cracker or not. This makes the "cracker method" an excellent way of setting the delay of the flash circuit. Note that the BB seems to move at about half the speed of sound in these pictures, since moving the microphone of the flash circuit an inch further away from the gun results in a picture in which the BB has moved about a half inch further away from the gun...

Digital cameras are a real boon to this process. With conventional (film) cameras, you carefully compute the required time delay, take a picture, develop the film in the darkroom, perhaps print a picture from the film, see if you got the timing right, adjust the timing, and try again. A tedious (and expensive) process, to say the least. Digital cameras make things much easier (and cheaper), because they provide "instant gratification" - you see the results of the shot as soon as you have taken it. This makes the job of setting the time delay much easier and faster.

It should be mentioned that safety glasses / goggles are a MUST when taking high-speed photos. Shattering light bulbs, bottles, etc. result in glass flying all over the place in the dark, and it's very easy for one of those pieces to end up in one of your eyes if they are not covered. Thick gloves are also recommended. While taking the pictures on this web page, I smashed, shattered, dropped, and shot bottles, light bulbs, compact disks, etc. Soon the entire floor of the garage was covered with wickedly sharp pieces of glass. When I got down on the floor to set up the next shot, it was very easy to put my knee or hand down on one of those glass shards in the dark and end up needing stitches. I made it a practice to sweep the broken glass pieces to the side of the garage after each shot, and I still managed to cut myself several times while taking these pictures...

Variable-delay flash circuits can be purchased from various web sites, such as Woods Electronics - Tools for high-speed photography and Kapture Group, Inc. However, if you have electronics experience, it's a lot cheaper to build your own. The November 1992 issue of Electronics Now has an excellent article on building your own variable-delay strobe circuit: "Build this Super Strobe - Create breathtaking stop-action photos with the Freeze Frame", page 31. This is the circuit that I used to take many of the pictures on this page. I discovered that this circuit (at least when it's built on a proto-board) is too slow to get good pictures of popping balloons, though, so I made my own circuit for that. Here is the circuit which I used for balloons. This circuit (when built on a proto-board) has a 15 microsecond delay between the start of the sound pulse from a popping balloon and maximum light output from the flash. Various web sites (such as HiViz - High-Speed Visual Imaging and Michael J. Brown's High Speed Photography) show other circuits, many of which are much simpler than the Electronics Now circuit.

Balloon popping seems to be a staple of high-speed photography. It is, however, much more challenging then it appears. Balloons pop extremely quickly - once the rubber of the balloon starts to tear, you have about a thousandth of a second before it's all over. In order to get pictures of a half-popped balloon, you need to trigger the flash as soon as the microphone detects the sound of the pop, with no delay. This requirement for a really fast-acting flash is what lead me to develop the circuit mentioned in the preceding paragraph. Below are several pictures of various balloons being popped by poking them with a sharp object.


Another way to pop a balloon is to inflate it with more and more air until the balloon just can't hold the pressure anymore and spontaneously pops via overpressure. This results in a significantly louder noise than you get when you pop a balloon by poking it. Also, when you poke a balloon, the balloon tears into 2 or 3 large pieces when it pops. When you pop a balloon via overpressure, the balloon shatters into dozens of small fragments. The following pictures are balloons that are being popped via overpressure. Note that these pictures are very different from the pictures above.


HiViz - High-Speed Visual Imaging has some excellent pictures of popping balloons that have had a small amount of corn starch placed in them. I attempted to replicate their results, but I don't think my pictures turned out as well as theirs did.


HiViz - High-Speed Visual Imaging also has several pictures of marshmallows being shot with a pellet gun. I used a BB gun and got similar results. Note that in the two pictures on the right, the marshmallow has been softened up by being microwaved for 5-10 seconds.


Here are several images of glass bottles being dropped onto the concrete floor of my garage from 4-5 feet up. Note the interesting shadows in some of the pictures. In the third picture, the bottle bounced without breaking. In that picture, the bottle is moving upward.


Here are several images of glass bottles full of water being dropped onto the floor from the 4-5 feet up. In the second two images, the water was dyed green with a little bit of sodium flourescein.


In this sequence, four different bottles full of water were dropped. The delay between the sound of the bottle hitting the floor and the flash was increased for each successive shot.


Here are three bottles being hit with a hammer. Note that the third bottle is full of water.


Here are various balloons full of water being dropped onto a wet floor from 3-4 feet up. Note that in the first picture, the balloon did not pop - it just bounced. The flying water is water that was already on the floor. In the second picture, the balloon did pop, but after the flash had fired. In the third picture, the yellow balloon is just beginning to tear around the edges (note little squirts of water near the top of the balloon). The delay between the balloon hitting the floor and the flash was increased a little bit for each shot in the sequence.


Here are various balloons full of water being shot with a BB gun. In all of the pictures, the BB is moving from the right to the left. Note that in the first six pictures, the BB is still inside the balloon. The delay between the gun shot and the flash was increased for the later pictures in the sequence.


Here are two balloons full of water being poked with a pin.


In this set of pictures, a BB is being shot through a compact disk. The delay between the gun shot and the flash was increased a little bit for each shot in the sequence.


This sequence shows a BB gun shooting a small paper cup with about an inch of water in it. Note that the faint stream of "smoke" coming from the barrel of the BB gun (in the lower right-hand corner of the pictures) is water vapor caused by a little bit of water getting into the BB gun. The delay between the gun shot and the flash was increased a little bit for each shot in the sequence. Notice how the hydrostatic shock causes the cup to jump off of the can.


This sequence shows a BB tearing its way through a saltine cracker the long way. In the first picture, the BB is just barely touching the cracker. In the second two pictures, the BB hasn't made its way all of the way through the cracker yet. The delay between the gun shot and the flash was increased a little bit for each shot in the sequence.


The left picture shows a BB going through an empty clear glass bottle. The right picture shows a BB going through a brown glass bottle full of water that has been dyed with a little bit of sodium flourescein.


For more information on high-speed photography, and for more pictures, check out the following links. Note that a Google search on "high speed photography" will turn up dozens of other sites...
The Edgerton Center at MIT
Andrew Davidhazy's High Speed Photography page
Student Projects in High-Speed Photography
Woods Electronics' primer on high-speed photography
Woods Electronics - Tools for high-speed photography
Kapture Group, Inc.
25th International Congress on High Speed Photography and Photonics

I will end by stating that any serious investigator of high-speed photography needs to get his hands on the high-speed photography book: "Electronic Flash, Strobe", by Harold Eugene Edgerton. Edgerton is the man who invented high-speed photography, and is still regarded as the world-expert in the field. Modern Photography magazine sums it up pretty well: "Written by the man who pioneered the method, who made the equipment, who made the early action-stopping photographs that amazed and inspired us, and who has 40 years of personal participation to report....Since one seldom finds so authoritative a writer in any field, it would be wise to pick this particular volume up and give it your thorough attention."