Never use full-output of your flash

[40Dude6aedyk]

Leo (aka PacAce) over on the lighting section pointed me to some discharge curves for a flash unit (see http://photography-on-the.net/forum/showthread.php?t=611152) which are probably pretty typical for a Xenon flash tube. The old discharge plots show that on full output the light output lasts more the 1/400th of a second, but that on truncated output (say 1/2 or 1/4 or ....) the flash duration is shortened to 1/1000th or 1/2000th.

Given that, it reads like one should strive to use strobes and speedlites at no more than 1/2 to 1/4 of output if you really want to stop action.

Questions: For all you strobists, do you typically use 1/4 or less output? Do you ever use full output?

Thanks!

[DDCSD]

It depends on the strobes. However, with many monolight strobes ( such as the Alien Bees) the flash duration gets longer when you use a lower power.

With speedlights, 1/4 or 1/2 power is better than full power.

[DC Fan]

For all you strobists, do you typically use 1/4 or less output? Do you ever use full output?

Full power output from a shoe-mounted flash happens all the time in the real world.

http://www.fansview.com/2007/metrocon/0708a0613.jpg

This image came from a 2007 event with stage lighting that basically was two shop lights. There was barely enough ambient light to get autofocus lock. The distances were 25-40 feet. To get a properly illuminated image, whether using a Canon 380ex or a Sunpak 383, either flash had to be discharged at full power.

Shutter speed and ambient light also are important in stopping motion with flash. If there's a lot of ambient illumination, something like the standard 1/60 flash shutter speed used by many Canon DSLR's can lead to ghosting from the ambient, and it's time to set the shutter speed to the body's maximum flash sync speed.

[DDCSD]

I'm pretty sure the OP is talking about for use in action sports where a slower flash duration will lead to ghosting.

[DC Fan]

I'm pretty sure the OP is talking about for use in action sports where a slower flash duration will lead to ghosting.

Agreed.

From experience, ghosting with flash and a relatively slow shutter speed can happen in any circumstance where there's plenty of ambient light, including stage presentations. People move during these presentations, and while the movement isn't as fast as during a sporting event, it's fast enough to produce ghosting. In the case of the image from the previous message, there wasn't enough ambient light on stage to cause ghosting - or to resolve a usable image with any lens on the market, for that matter.

Your average basketball gym will have far more ambient light, enough to let you get decent images with a 50mm f/1.8, or even with a slower lens if the ISO is bumped up to 1600 or so.

[40Dude6aedyk]

f/1.8 results in a DOF that is too shallow. So while you give up ghosting, you have body parts OOF.

[DC Fan]

f/1.8 results in a DOF that is too shallow. So while you give up ghosting, you have body parts OOF.

Is depth of field a question? Now you've raised another series of factors. If you want broad depth of field, you need a small aperture, which means more light, which means you'll probably need to discharge any flash or strobe you want at full power. If you want to use less flash power, you'll have an underexposed image at the small aperture that means greater depth of field - unless you use a high ISO, which some may not like because it's noisier than a low ISO.

All of these things are interconnected, and one change leads to others.

[Zivnuska]

Your full power duration on the 580 is 1.2 ms (about 1/800 sec). Lower powers take less time on a speedlight.

[40Dude6aedyk]

Your full power duration on the 580 is 1.2 ms (about 1/800 sec). Lower powers take less time on a speedlight.
The 1.2 msec duration is what the manual says. That might be Japanese for 5 msec. In other words, I don't believe that number, especially in light of the thread linked in the OP.

[Zivnuska]

There are flash duration measurements that are widely differing on the web. It is hard to know which one (if any) to believe.

http://www.photosbykev.com/wordpress/2008/07/12/canon-580ex-flash-duration/