How does flash duration and freezing movement depend on the model, type and power output of your flash units?

This weekend shooting a jumping model into the sunset created images failed  in freezing motion.  Further, the heavy DOF (depth of field) of shooting at F22 rendered dust on the lens filter easily visible throughout the blue sky.

Motion Blur using Studio Flash and Dust visible on lens filters stopped down to F22 Tokina 11-16mm

Studio Flash, Clearly Visible Motion Blur in the eyes. Arrow points to sample of Lens Dust F22 @ 11mm Tokina Zoom. Click to see more details.

Equipment:

Being interested in the topic of high-speed photography generally and wishing to remedy issues in my weekend photography, I did a bit of research and learned a few things about flash durations.

During my shoot, the Buff X3200 flash unit was being fired around 1/2 power.  Exposure settings were ASA 200, 1/100 second and F22.

This created two problems for me (see sample shots):

  • Motion blur – model’s face is clearly blurry, most noticeable in the eyes
  • Heavy DOF (depth of field) brought into focus dust on lens protector

Okay, I can fix the dust issue in photoshop or by cleaning my lens.  Still, shooting outside, we were in a dusty environment.  When you shoot a wide angle lens stopped down to F22, you often will see in your images whatever is on the lens surface.   Open up your aperture a bit if you can.   Do what you can to keep clean or fix it in photoshop if you can’t…

The issue of the motion blur is a bit trickier.

My studio flash, generally and as is typical,  has longer flash durations than my Nikon SB600 Speedlight.

The SB600 has rated flash duration ranges from 1/900 second at full power down to a blazingly fast 1/25000 second at 1/64 power.   For these Nikon speedlights, the lower the power output, the faster the flash duration.

My Paul C. Buff studio flash units work in an entirely different manner.  The higher the power output, the longer the flash durations for these studio flashes…

It turns out the X3200 has a rated flash duration from 1/900 second at full power to 1/450 seconds at 1/32 power.   The X3200 also has separate 1/4 power range settings.  In the 1/4 power range settings, the rated flash duration are shorter:  1/3300 sec at 1/4 power down to 1/1650 second at 1/128 power.

I was shooting at roughly 1/2 power or perhaps about 1/500 second.  Not enough to stop motion blur.

Alien Bee 800’s have shorter flash duration ratings of 1/3300 second at full power to 1/1650 second at minimal power.  The Alien Bee 400’s have even shorter flash duration ratings in the range of 1/6000 to 1/3000 second from full to minimum power respectively.

In publishing ratings, the standard  t0.5 rating rating is used.  What this t0.5 (or t.5) means is the amount of duration of flash above 50% of the maximum light output.

The flash, as it is triggered, gets brighter and brighter to a peak brightness, then gets dimmer and dimmer.

t0.5 is the time the flash is more than 50% of its peak brightness.

A jumping person might be traveling at about 2 meters per second.  This works out to 2000 millimeters per second or 4 millimeters (mm) per 1/500 second.

4 mm is about 3/16 of an inch.  Clearly a visible movement amount.

Another interesting measure of flash duration is t0.1 (or t.1).

t.1 is the amount of flash duration above 10% of maximum light output.

When using flash to freeze motion, t.1 is the usually the more useful indication of stopping power.

t0.1 is typically about 3 times the length of the industry standard rating of t0.5.

The Cyber Commander has a flash meter which includes a t0.1 flash duration measurement.

The X3200 at full power has a measured t.1 of about 1/125 seconds.  At half power, t.1 measures about 1/200 of a second.  This is 3/8″ of motion for my jumping model.

Any wonder she is blurry?

When using the Cyber Commander to measure the X3200 in the 1/4 power range set to full 1/4 power, t.1 comes in at 1/1000 seconds.

A Nikon SB600 Speedlight at full power is about as slow as the X3200.  The X3200 in 1/4 power mode at the full 1/4 power setting is faster than the SB600 at full power.  The SB600 in lower power modes is the fastest and dimmest of my available choices.   If I can live with its lower power output and a speedlight’s lighting quality, the SB600 becomes my go to light.  And so on.

Doing this shot again, I might shoot try using the high end of the 1/4 power mode of the X3200, or may try using my Nikon SB600 .

What I may not be able to do is to get the light output needed to overpower the sun and stop motion both at the same time.

There remain several more tests to run and choices to make.

In short, to freeze motion using flash, it is essential to know how each particular piece of gear operates and then fit this capability into our overall compositions.

Know your gear and consider this topic of flash duration and motion blur when seeking to capture or freeze action shots using flash, both in your selection of flash unit (AB400 may be a better choice than the X3200) and in the power output and exposure setting selections for your particular rig.

Please share your experiences and opinions?


 

 

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One Response to How does flash duration and freezing movement depend on the model, type and power output of your flash units?

  1. This was very useful! I will recommend people to read this if they want to understand strobe lighting. :)
    I have had the same issue with blurred shots when I shoot using both ambient light and stobelighting, I believe that it is because the camera manages to “see” more than only what the strobes enlighten. That means that the shot you used as example actually has frozen the moment with only 1/100sec, even if your strobes where set to 1/500.
    If you wouldn’t have used the strobes, you would still have seen the landscape, and probably the model as well.
    It would helped a lot if there would be no direct sunlight on the model, only at the background, you can do that by building a partytent around her or something, or just stand behind a tree.

    Try once to set your camera so fast that you’d get a black image without strobes, and than pump up the power of the strobes a little. Then you’ll get an image that is frozen by the strobes.
    And when you get a hold of strobes that fire at 1/2500 or more at t0.1, the result will be chrystal sharp.. :)

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