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Can wireless flash triggers decrease the camera's actual sync speed?

I am using a set of YN-603 triggers to trigger a YN-560II with my D5100, but it looks like when I have it set as 1/200s I get a small black band at the bottom of the picture. Is it due to the wireless triggers? Does that mean my actual sync speed is lower than 1/200? Or is my camera faulty? How can I check?

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May I ask why you need to shoot at a speed >= 1/200 second? The flash duration is far shorter, so subject motion should be minimal. –  Steve Ross Jun 8 '12 at 18:08
To be able to shoot in daylight with a wide aperture and use the flash as fill-flash. –  Weboide Jun 15 '12 at 12:54
Higher shutter speeds reduce the effect of ambient light and rely more on the flash. To use the flash as a fill, open the lens, as you say, and reduce the amount of flash using flash exposure compensation until you are happy with the result. If you aren't able to use the wide aperture (and really want one) because the ambient light is too bright, consider using a neutral density filter. –  Steve Ross Jun 15 '12 at 18:27
Thanks Steve, that was really helpful. –  Weboide Jun 20 '12 at 17:38

2 Answers 2

up vote 5 down vote accepted

The sync speed itself doesn't change, as that is defined by how quickly the shutter curtains move, but what is happening is the trigger is adding a delay, which throws off the timing. What ought to happen at 1/200s is that the first curtain reaches the top, the flash fires, then the second curtain starts closing immediately from the bottom. However due to the delay the second curtain has started to close by the time the contacts close on the remote flashgun, blocking part of the frame and giving you a black bar.

The delay is caused by the trigger needing to decode the signal and close a switch to fire the flash. The length of the delay is depends on the brand, and sometimes how much battery power is left in the trigger, but what you describe is common for that brand of triggers. I used to always set my shutter to 1/160 to be on the safe side.

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I guess we could call it the effective sync speed, and that would be 1/160s with my current gear. Could I reach the possible 1/200s using optical slave, since no wireless triggers would be involved? –  Weboide Jun 8 '12 at 16:26
@Weboide It depends on how quickly the transistor in the optical slave can switch, but it ought to be several orders of magnitude faster than decoding a signal using an IC so I would imagine you ought to be able to shoot at 1/200s using an optical slave. –  Matt Grum Jun 8 '12 at 16:44

Well. the max sync speed presupposes that the slave flash reacts instantly to the trigger. If it takes any amount of time at all for the slave to react, that is going to eat into your sync speed as the second curtain will have started to close before the slave flash actually fires.

So I'd say that yes, you would be better off to back off some from max sync when using slave flashes.

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