Ok, so if you want to freeze action outside using both sunlight and flash, you’ll need to use a high shutter speed to freeze those parts of the subject that are lit by the sun – as its a continuous source. Sure you may be able to light the subject in such a way that they are dominated by flash, and use a regular x-sync compatible shutter speed to freeze your subject with fast flash, however to get them completely frozen, you’ll need to freeze all the light with a high speed shutter – say 1/4000th of a second. We know we can use compatible Speedlights for this with High Speed Sync (HSS pulses the light to share it out over the entire shutter operation – to act like a bright continuous light) however this is only possible with certain Speedlights. If you need more power, you can always tape more Speedlights together, however sometimes its more convenient to use one big light: you can configure it quicker and use all manner of modifiers on big lights.
However – there is another way. Big old long duration studio lights have a long tail of light that takes a while to die away. If we open and close the shutter at the exact right time, after the initial peak of light, and just use the tail-off, it’ll be pretty even across the frame. This is known as Tail Sync. All we need then, is a way of delaying the shutter operation. A number of radio trigger systems based on the 2.4GHz frequency are fast enough to do this. Pocket Wizard III’s can do it, and so can the Yongnuo YN622N triggers I use on my Nikon Speedlights. I have some old and very slow studio lights (CF-D300’s from Viewfinder) so I thought I’d try some tests. Yongnuo call this “SuperSync”. First – some control tests using the regular radio triggers:-
From left to right: 1/160th, 1320th and 1/640th of a second. By 1/640th of a second shutter speed, the rear curtain has almost closed by the time the light gets out there. Now we’ll swap over to a YN622N on the strobe, and a YN622N-TX on the camera. The receiver is on channel 1, group A and I have group A set to manual on the YN622N-TX. The strobe is on minimum power – just as it was for the control shots.
The shutter speeds go from 1/640, 1/1250th, 1/2000th, 1/4000th and 1/8000th in these shots. The subject is the actual receiver that is connected to the sync port on the strobe. As I took a stop away by doubling the shutter speed each time, I put this back by opening up the lens until I hit f/1.8 and then started doubling the ISO instead, so the exposures should be roughly the same. In the last shot, I stopped down to f/8 again, put the ISO back to 100, the shutter at 1/1250th and turned the strobe up to full power. I didn’t need to touch anything on the trigger to make this happen – it automatically switches to tail sync or HSS depending on what is attached to the receiver when it sees a shutter speed on the camera that is out of bounds (you can set this value on Nikon bodies and mine is set it to 1/160th when I have the camera in “studio” mode, and 1/250th in the “normal” settings bank). The letters “FP” appear in the YN622N-TX display when the shutter speed is above the X-Sync value. Next I tried my new state of the art IGBT driven Lencarta 600-SF strobes. Now these work like Speedlights and have a very brief flash duration at lower outputs as they have the ability to cut the light off dead rather than letting it tail off. So tail sync will only work at all at full power, and even then they are much faster than the old style lights. Tail sync still works, although you need to be even more precise with the timing:-
The difference in these 2 shots is achieved by manually varying the delay on the YN622N-TX. By doing this you can move the window of light about: see how the light is visibly higher up the frame on the first shot (left) as it has fired later than in the one on the right. Remember that outside, we will also have ambient light so this is not as critical – these test shots are pure flash, and the light is only skimming the background. Just to see what would happen, I turned the 600-SF down to minimum power (where it is fastest) and as expected, we illuminate only a fraction of the frame that is between the shutter curtains at the time of the flash.
Note how by altering the sync delay on the trigger, I can choose where the slit appears: adding less delay moves it up the frame (the top bar is the front curtain and the bottom bar is the rear curtain. Other makes of camera may have the curtains travelling down instead of up , or from side to side etc). The with less delay, the curtains have moved further before the flash starts. With the right heads though, it works well – in fact I’m surprised just how well this does work, and how seamless and easy it is to setup. The YN622N system also allows you to mix this SuperSync activity with iTTL and manual Speedlights, all in the same exposure: e.g. one group set to SuperSync controlling any amount of old strobes, and the other 2 groups set to iTTL or manual with CLS compatible Speedlights attached to the receivers. Next stage is to test this outside the next time we have some strong sunlight, to see if there’s enough useful power to compete with the sun at fast shutter speeds.