High Speed Photography With Your Flash

If you’re looking for a photographic challenge to spice up the new year, you might consider high speed photography. When you hear the words “high speed”, the first knob you might reach for is the shutter speed. Unfortunately, as you will soon find out, this knob is virtually useless. While a shutter speed of 1/8000 sounds fast, you will find that most cool things in life happen much faster than that.  And unless you’re taking photos on the surface of the Sun, you will also find that there is never enough available light for such a fast shutter speed.

The best way to freeze action in high speed photography is not with a fast shutter speed but with a flash. A flash freezes action by illuminating a moving scene for only a split second. Any pre-flash and post-flash movement then recedes into relative darkness and is unrecorded on your camera sensor.

The first lesson of high speed flash photography is that not all flash pulses are created equally. You know, of course, that you can adjust the flash discharge to suit the scene of interest.  You may not know that many flashes accomplish these exposure adjustments not by changing the intensity of the light pulse, but by changing the duration of the light pulse.  This explains all those flash photos you have taken which still contain motion blur.  Photos taken with a flash at full power will have a relatively long duration light pulse and it will be very hard to freeze the action.  The best way to stop motion in your images is to turn your flash down to its lowest level.

We’ve demonstrated the flash duration effect below with a simple experiment.  A computer fan was outfitted with a solid black disk with a thin white line on one radius. The motion-freezing ability of different flash settings was then measured by observing the length of the arc swept out by the rotating fan during the flash pulse. The flash used for this experiment was a Canon 580EX II.

With each successive reduction in flash power, the thin white line becomes ever more clear as its motion is frozen.  At 1/16 power, we begin to reach a point of diminishing return but subtle improvements in clarity can be observed all the way down to 1/128 power.  It may be surprising to note that the shutter speeds for all these images were greater than half a second. Since the flash was supplying all the light for the image, shutter speeds were almost inconsequential.

Still think you could get the same result without a flash?  Here’s the same scene photographed using a 1/8000 shutter speed without a flash. Even after several hot lights were brought in to allow a decent exposure, the motion stopping power is poor and there is a substantial rolling shutter effect.

So what are the effects of flash duration on a real scene? The water drop photos below were taken with taken at full power (left) and 1/32 power (right).  While the left image shows significant motion blur, the right image is perfectly frozen.

NOTE: For images such as the water drops below, a high speed trigger will help you time your flash with the action.  DIY fans might enjoy this set of products while a more sophisticated turnkey option can be found here.

Of course, there are also penalties for using a low power flash. It is vital to have the flash as close to the subject as possible.  Reflectors may also be needed to help to efficiently use all available light from the flash to illuminate the subject.

High speed photography is a great way to to flex your creative muscles on some scenes you might not otherwise think about.  Water drops, popping balloons, breaking wine glasses….the possibilities are endless.  Here’s to a new year of photographic challenges!

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