[mattb123]

I have a couple of P-TTL flashes, a sigma 530 Super and a relatively new Metz 58 AF-2.
When I shoot something with fast action I often put the flash in HSS or FP mode (same mode, different term for each of the two brands I own) so I have have a flaster shutter speed. This generally works but I wish I had more output. I realize why I don't (multiple pulses) and that makes sense.

So I had a thought about a workaround using two bracket-mounted flashes and a Y TTL cable to connect both flashes and then run them both in HSS/FP mode. Would that work? Does the camera need much back from the flash in terms of data or is communication pretty one-way?

If it might work, is there a cable to connect two flashes to a single hotshoe?

Thanks!

[manacho2005]

Have you tried them as wireless slaves in HSS/FP? I believe both of those flashes can do it.

[Class A]

So I had a thought about a workaround using two bracket-mounted flashes and a Y TTL cable to connect both flashes and then run them both in HSS/FP mode. Would that work?

Seems unlikely to me that a Y-cable would work with P-TTL.

The camera and flash are communicating digitally, sending data back and forth.

I don't think two flashes could be that well synchronised that they would send they same data at the same time.

Either use optical triggering, or add manual (non P-TTL) flashes. The latter would either have to run at full power to generate a long pulse (but you'd still see a fall off over the frame as the pulse intensity dies down over time) or you use flashes that can be set to HSS mode manually. I know the Cactus RF60 can do this and I believe the Godox V850 can as well, but I'm not entirely sure about the latter. The V850 may needs the Canon-only "Cells II" trigger for generating an HSS signal.

[mattb123]

Thanks guys. Optical slave triggering in HSS/FP is probably my best bet. I'll give that a try sometime and report back. I also have a simple optical trigger that I could try with a flash in full power manual mode, I just figured the timing would be off. Maybe that is worth a shot as well.

I also need a good bracket that can take two flashes without being too expensive. Any recommendations?

[bdery]

Have you tried them as wireless slaves in HSS/FP? I believe both of those flashes can do it.

What he said. Simple, efficient, it will just work.

[manacho2005]

http://www.amazon.com/Generic-Double-Extension-Bracket-Compatible/dp/B00DO0O36U
I'm not sure if it would allow the pop up flash to fully open, though. You will need that for wireless sync...

[JimJohnson]

When I shoot something with fast action I often put the flash in HSS or FP mode

I'm not sure you realize that HSS is not meant for using your flash for fast action?

The curtains in your camera ALWAYS take 1/180th of a second to cross the sensor plane, no matter what shutter speed you use. Therefore, 1/180th second is the fastest speed in which the shutter opening is fully open. Your flash fires once while the shutter is completely open. As noted, so long as ambient light contributes little to the exposure, the much faster electronic flash will perform stop-motion photography.

For all shutter speeds faster than 1/180th you have a moving slit as the trailing curtain chases the leading curtain across the face of the sensor. How HSS works is to repeatedly strobe your flash as the slit crosses your sensor.

For still subjects this allows you to use a higher shutter speed to offset ambient light. However on moving objects, depending on the direction of movement, you get multiple exposures of the moving object, once per flash strobe, as it moves. You can turn this into an artistic advantage, but it won't help at all if your intended purpose was to perform stop-motion photography.

[mattb123]

I'm not sure you realize that HSS is not meant for using your flash for fast action?

Well that is a good point. Thanks for the reminder. I think it may depend on how fast the action is because I have had some success doing that. It seems like if the multiple pulses are faster than something like a 1/500 shutter speed they wouldn't be visible in a lot of cases.

It can be tough to stop action at 1/180 when I need fill flash. What other options do I have?

[bdery]

It can be tough to stop action at 1/180 when I need fill flash. What other options do I have?

Boost the ISO or, indeed, use HSS while understanding the limitations.

[JimJohnson]

It can be tough to stop action at 1/180 when I need fill flash. What other options do I have?

Set your shutter manually to 1/180th second and stop down until your background is slightly underexposed. The flash then becomes your effective shutter speed for your subject. It is far faster than even the highest camera shutter speed and will freeze the action.

Taking this same technique to extreme is how they capture a bullet piercing a balloon. In this scenario, the shutter is on bulb in a very dark location. The flash is so short that it can freeze a bullet.

It always takes at least 1/180th second for a complete exposure with your camera. That is the mechanical speed of the leading and trailing curtains. Shorter exposures are accomplished with a moving slit between the two curtains. If you are able to freeze a moving subject using HSS, you should be able to also freeze the same subject at 1/180th second.

[Class A]

It is far faster than even the highest camera shutter speed and will freeze the action.

Flash duration depends on the flash power, though.

A typical flash gun will take ~1/125s for a full power pulse.

At 1/4 power a Metz 58 AF-2 still has a T.5 time of 1/1500s, at 1/32 it is 1/9000s, and at 1/256 it is only 1/33000s.

If you are able to freeze a moving subject using HSS, you should be able to also freeze the same subject at 1/180th second.

While it takes 1/180s for the full sensor to be exposed, any particular area of the sensor is only exposed for the specified shutter time. Ergo, you can stop action locally but you will get an effect similar to the "rolling shutter" effect in video recordings. Different parts of the scenes will be recorded at different times so there will be skewing effects, but the level of local blur should be limited by the actual shutter speed.