Hygh Speed Sync with 580 EX II question

Started Aug 8, 2009 | Discussions thread
Anonimo Contributing Member • Posts: 583
Keeping it simple

Holla Edgard!

HSS is not intended to have any esthetical effect on your pictures.

HSS just enables shutter speeds faster than the x-sync when you use flash. If the x-sync of your shutter is 1/250s then:

  • with HSS off: you cannot shoot faster than 1/250s

  • with HSS on: you can shoot faster than 1/250s but at these faster speeds the flash guide number will be lower than it would be at slower shutter speeds (for same power output). the faster the shutter, the lower the guide number.

HSS brings no disadvantage but if you are far away from your subject you might preffer to stick with shutter speeds lower than x-sync to get the full guide number. Some people recommend to disable HSS to prevent the camera to pick a faster shutter in these situations.

Why that?

  • When the shutter is slower than x-sync the flash is fired once, while the frame is fully exposed to the light.

  • At shutter speeds faster than x-sync the frame is never fully exposed to the light. Instead, only a slice of the frame is exposed at each time.

  • HSS copes with that by firing the flash multiple times. If x-sync is 1/250s then the flash fires 16 times during 1/250s to cope with a shutter speed of 1/4000s The guide number at full power and 1/4000s will be equal or lower than the guide number at 1/16th of full power at shutter speeds below 1/250s.

Good Luck!

Edgard wrote:


I'm having problems understanding High Speed Sync with my Speedlite 580EXII. I though HSS was a feature aimed at outdoor shoots when you need to under expose the background and freezing motion. I don't understand why I get more flash output without HSS at slower shutter speeds.

Here are two examples with flash set to manual at full power.

Is not supposed to be the opposite and get more flash influence with HSS ?


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