Flash duration experiments

Started Mar 3, 2012 | Discussions thread
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jean bernier
Veteran MemberPosts: 3,163
Flash duration experiments
Mar 3, 2012

Some of you might have seen such experiments, but here is mine. Have made a lot more shots than these, but I posted the most interesting cases.

A fan was photographed backlit using a D3X at 1/60th (recording most if not all of the flash duration)in order to see what is the real life action ability of some of the flashes at my disposal. Flash duration is often an overlooked specification when comes the time to choose a flash system. Manufacturers do not help by specifying the duration in the form of the meaningless t=0.5 format, while the real life spec should be t=0.1 to be of any use. If not specified, the duration is most likely t=0.5 wich makes specs look impressive, but is deceiving.

Divide the unknown spec by 3 and you should be in the ballpark of true flash duration, and therefore of comparable continuous light shutter equivalent. A "1/1000th" t=0.5 studio flash has really only a 1/333th t=0.1 duration. Upping the shutter sync speed to 1/250th cuts in the actual duration, lowering overall brightness, but worse, the second curtain travelling while the flash slope is still present produces unevenness, especially visible on seamless backdrops. A leaf shutter only cuts in the brightness.

You'll notice that a speedlight such as the SB-800 shows the typical studio flash long slope behaviour: it only cuts the slope starting at half power. Probably, the reason there is no setting between Full and Half Power is the semiconductor is incapable of dealing with the intense current. Some rare studio flashes do actively cut the flash duration, just like in a speedlight, and manufacturers proudly publish t=01 specs; the AB instein does that, and at the other end of the spectrum, the very expensive and amazing Broncolor Scoro.

Jean Bernier

All photographs are only more or less credible illusions

Nikon D3X
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