How do I freeze the movement of my subject when using electronic flash and what is all this hype about effective flash duration?

Today most electronic flash manufactures are using the effective flash duration. This is defined in ISO Specification 2827,3.9 as "Effective flash duration is the time interval from the instant the flash reaches one-half of its peak intensity to the instant it decays to the same value."

All that sounds very technical but how the heck can I get a shorter duration to freeze the action of my subject and eliminate blurring & ghosting.

Let's say your electronic flash is a 2400w.s. power pack and the manufacture states that the effective flash duration of 1/400sec with one head at full power. The power pack has 4-flash head outlets and a voltage control power variator adjustable from full-1/8 power level. You take a shot at full power and the picture is very blurry.

You then turn down the power variator all the way to 1/8 power and again same results. Does this scenario sound familiar?

Please tell me what do I have to do to get a shorter duration, add more flash heads and turn the power variator back to full power.

If the effective flash duration is 1/400sec at full power with one flash head, then it will be 1/800sec with two flash heads, 1/1200sec with three heads and 1/1600sec with four heads. That's four times as fast when using four flash heads at full 2400w.s.

Will the effective duration get shorter if I use four heads and turn the voltage control variator to a lower power level?

When a power variator is controlling the voltage on the capacitors and the power output is lowered the effective flash duration has only a very slight or no change. The down side to this is that you are reducing the light on the subject.

If a shorter duration is require then use a 1200w.s. unit with four heads as stated above. If the effective flash duration @1200w.s. Is 1/600sec with four flash heads it will be 4 times as fast, 1/2400sec.

Please Note: Some power packs have capacitor switching and by lowering the overall power a shorter duration can be achieved. The Sun Star Strobo VP-Series power packs have capacitor switching, please refer to the flash duration chart under Specifications.

I did just what you said in the above information and I was able to freeze the action but I am now getting ghosting. What's up!

The ghosting can and will be eliminated when you light the background with the same short effective duration as the subject light. Use another 2400w.s. Power Pack with four heads to light the background.

Sun Star Strobo Mini Series and Magnum Series Power packs have short effective flash duration's and by using one Y cable box per Power Pack the duration will even be shorter.

If you have any questions please give Larry Farrell a call at 1-888-999-4598 or send an e-mail to sales@sunstarstrobo.com

Courtesy of Larry Farrell, Sun Star Strobo Flash Lighting Systems.

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