# HSS power loss



## climber (Aug 18, 2014)

Is possible to say how big is the power loss of a flash while using HSS compared to sync speed?


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## Jim Saunders (Aug 18, 2014)

Sure, set a scene at whatever your sync speed is and f/14 or so, whatever fixed ISO you need and manual flash output. After that go to HSS and see how much you have to open the aperture to get the exposure back up.

Jim


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## climber (Aug 18, 2014)

Thank you for that advice. 

And let say, if I have to go from f/16 (at sync speed - 1/200s) to f/8 at HSS to get the same result, that means, the flash has half output power at that speed sync?


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## Jim Saunders (Aug 18, 2014)

Your exposure changes by a factor of two for each stop, so the two stops between f/16 and f/8 means your flash delivers a quarter of the power. The math aside if you know that going to HSS means two stops (or however many) then you have the answer you need.

Jim


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## privatebydesign (Aug 18, 2014)

Going into HSS costs me 2 stops. So 1/250 sync speed at f8 equals f3.5 at 1/320 (one third of a stop over sync) the power loss is 2 and 1/3 stops but you also went up 1/3 stop of shutter speed, so two stops loss of power.

Each additional stop of SS costs another stop of flash power.


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## climber (Aug 18, 2014)

privatebydesign said:


> Going into HSS costs me 2 stops. So 1/250 sync speed at f8 equals f3.5 at 1/320 (one third of a stop over sync) the power loss is 2 and 1/3 stops but you also went up 1/3 stop of shutter speed, so two stops loss of power.
> 
> Each additional stop of SS costs another stop of flash power.




So, let say I need f/11 at sync speed (1/200s) at full power flash. I want to shot at 1/800s, which is 2 stops less. What would be the math in this case. What f number do I have to dial in and what would be the power of flash in this case (relative to the full power from the first case).

Thanks


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## privatebydesign (Aug 18, 2014)

climber said:


> privatebydesign said:
> 
> 
> > Going into HSS costs me 2 stops. So 1/250 sync speed at f8 equals f3.5 at 1/320 (one third of a stop over sync) the power loss is 2 and 1/3 stops but you also went up 1/3 stop of shutter speed, so two stops loss of power.
> ...



f11 @ 1/200 (sync) 1:1 flash and iso 100 would equate to

f2.8 @ 1/800 1:1 flash in HSS and iso 100

You lose four stops of flash power, two for going into HSS and another two for going up two stops of SS.

Even though your flash is firing at full power you are getting an effective 1/16 of actual light.


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## climber (Aug 18, 2014)

privatebydesign said:


> climber said:
> 
> 
> > privatebydesign said:
> ...



And you don't take into account that you also have wider aperture for 4 stops (from f/11 to f/2.8)?


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## privatebydesign (Aug 18, 2014)

That is being taken into account by your power loss. HSS costs a lot of power!

I just tested it and it is true too.

1/16th flash @ 1/200 and f11 gives the same illumination as 1/16 flash @ f2.8 and 1/800 sec.

If you put the flash to 1:1 in the above scenario in HSS then you get around 1/3 to a half stop more light at 1/800; so the 1/16th flash @ 1/200 and f11 is slightly darker than 1:1 flash in HSS @1/800 but thinking two stops loss for HSS PLUS the additional stops of shutter speed will get you within a 1/2 stop.


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## climber (Aug 18, 2014)

Thank you, now I understand.


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## Skirball (Aug 19, 2014)

Why not take a photo at max sync speed, then just go up 1/3 a stop and see the difference between single pop and HSS. It would minimize the impact of shutter speed, which will directly affect exposure in HSS. Once you establish that difference you know that you'll lose a stop every time you go up a stop in shutter speed.


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## privatebydesign (Aug 19, 2014)

Skirball said:


> Why not take a photo at max sync speed, then just go up 1/3 a stop and see the difference between single pop and HSS. It would minimize the impact of shutter speed, which will directly affect exposure in HSS. Once you establish that difference you know that you'll lose a stop every time you go up a stop in shutter speed.



That is exactly what I dd in my first reply. Going up 1/3 stop above sync cost 2 and 1/3 stops of power.



> Going into HSS costs me 2 stops. So 1/250 sync speed at f8 equals f3.5 at 1/320 (one third of a stop over sync) the power loss is 2 and 1/3 stops but you also went up 1/3 stop of shutter speed, so two stops loss of power.
> 
> Each additional stop of SS costs another stop of flash power.


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## Skirball (Aug 19, 2014)

privatebydesign said:


> Skirball said:
> 
> 
> > Why not take a photo at max sync speed, then just go up 1/3 a stop and see the difference between single pop and HSS. It would minimize the impact of shutter speed, which will directly affect exposure in HSS. Once you establish that difference you know that you'll lose a stop every time you go up a stop in shutter speed.
> ...



Sorry, you're right. I saw a bunch of discussion involving changing the aperture and shutter speed and whatnot and it seemed to be over-complicating things.


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