HSS off camera?

[mattfisher5]

Hello,

I am new to using speedlites and I am a bit confused about whether or not I can use HSS off camera. I am planning on purchasing YONGNUO Wireless ETTL Flash Transceiver YN622C II with High-speed Sync HSS 1/8000s. I would like to place one transciever on my camera, and one on the flash, off camera. Would the 270 EXII, 320 EX, or 430 EXII work with HSS in this scenario?

Thanks,

Matt

[Waddizzle]

Before you can get a helpful answer, it would be helpful to know what camera you're using, too. 

BTW, maybe it would be best if you asked YONGNUO about their gear, and how compatible it is with Canon gear.

[mattfisher5]

I am using a T5 rebel. Yongnuo lists the 600, 580 EXII, 430 EXII, 320 EX, and 270 EXII as being compatible with their transcievers. The Yongnuo brand flash units that are compatible with these transcievers all state that the flash unit is capable of HSS at 1/8000. However, under the specifications section on the page for the 320 EX, it states HSS (1/250). This is what initially confused me as to whether with the Yongnuo transciever attached, it would be capable of 1/8000, or if the Yongnuo transciever is just capable of triggering the flash at the highest capable sync speed of the flash, being 1/250 in the case of the 320 EX?

[Waddizzle]

Seeing how the camera is incapable of 1/8000, I would seriouly doubt it.

[mattfisher5]

Yes, I believe the T5 max shutter speed is 1/4000th. So I know I would not be able to reach 1/8000th with my camera, but I would like to be able to get around 1/1000th or so. And I would like to have the ability to reach 1/8000th with the speedlite setup if I upgrade bodies in the future.

[TCampbell]

Even when HSS is used, there's still always a limit based on how much flash power is needed and subject distance.

When you shoot at or below the flash sync speed, the shutter completely opens, then the flash fires, then after the exposure is finished the shutter can close.

When you shoot at any speed above the max flash sync speed, the 2nd "curtain" of the shutter is chasing the 1st curtain ... so a gap is sweeping across the sensor.  At no point is the entire sensor ever exposed to light at these speeds.  This implies that no matter when the flash fired, some part of the sensor would be covered by a shutter curtain.  In HSS mode, the flash pulses rapidly as the shutter opening sweeps across the sensor.  

However there is some amount of power needed to adequately illuminate a subject and then there's some maximum amount of capacity that the flash can hold in it's capacitors for the shot.  In other words if the subject actaully requires about a 50% power burst to be correctly lit then the flash can only burst twice and it's spent 100% of the power.  If you speed up the shutter such that no more than 1/4 of the shutter is exposed then the flash would minimially have to fire at least 4 times and it doesn't have enough of a power reserve to fire 4 times (in my scenario.)

I have no experience with Yongnuos.  But with the real Canon system you can cluster mlutiple flashes and the ETTL system knows how to do this automatically.    This means that even if you're beyond the limits of what any single flash could possibly do, you can throw enough hardware at the problem to solve it (you can cluster up to 15 slave flashes off a single master).