dmward wrote in post #18602002
I am always taken aback when people say that HSS cuts the flash power.
What HSS does is spread the power in the capacitor over the duration of the shutter curtain travel across the sensor.
Its a distribution of power over a longer time than the peak and fade distribution for normal x sync flash duration.
Like any constant light source, when the shutter speed increases, shortening exposure and narrowing the slit between leading and trailing curtains, there is less time for the light to energize the sensor. That's not the flash losing power, its the exposure triangle operating as expected with a constant light source.
it is true that the amount of 'electrical power' is the same whether in HSS or not....there is a single capacitor used for both modes, and it has a finite amount of electrical power.
However, the light output power is indeed diminished by -2EV or -3EV (the amount dependent upon flash, even two units of the same model are known to vary from one another!), so with regard to useful light intensity there is indisputably a POWER DROP due to HSS. And that is why the range indicator on the back LCD of a Canon 580EX diminishes in distance, as the light intensity has diminished so it cannot reach as far at the identical f/stop.