W/S question

How many Watt/Seconds has a 430ex?

It's hard to compare a speedlight to a strobe in terms of w/s because the flash head design. For practical purpose, I did use a light meter to measure the light bouncing off an umbrella. Compare the f stops and w/s rating of a strobe, my estimate of the 430EX is about 30-40 w/s.

so a AB400 would be 4 to 5 time stronger, right?

I estimated the power of my 580EX II to be about 40 watt-seconds. Flash meter testing revealed that it produced 4 stops less light than my B1600 (640 watt-seconds) when fired into the same umbrella.

By squaring the guide numbers and dividing them, you can estimate that a 430EX has about 55% of the power of the 580EX II.

That would put the 430EX at around 22 watt-seconds.

The B400 (160 watt-seconds) is over 7 times more powerful. In other words, it would take seven 430EX flash units to approximate the light output of the B400.

Keep in mind this is merely an estimate, and a strobe's watt-second rating is a measurement of the energy it uses, not a measurement of the light it produces.

thanks