Recently, I came across a comment on Facebook that said it was possible to get shutter speeds faster than the native sync speed by using a High Speed Sync compatible flash to optically trigger your studio strobe. The topic came up again at the APPA Spring Seminar where a Paul C. Buff Einstein was used in High Speed Sync mode to capture images of dancers in clouds of flower petals and flour. The question was brought up if this was possible to shoot without the Einstein and HSS radio trigger. I mentioned using hypersync, and tried to explain the idea briefly. With it being a somewhat complicated topic, I felt it would be easier to explain if I went through it in writing.
Here's the theory behind hypersync. Without the use of special HSS radio triggers, your strobes are locked into the native sync speed of the camera, typically a shutter speed of 1/200 or 1/250. The camera is programed to send the signal to fire your flash as the first curtain fully opens and the second curtain hasn't started moving. Once your shutter speed is faster than that sync speed, the second curtain starts moving before the first curtain has completely opened, therefore, there is not a moment when entire sensor is exposed to the flash. HSS overcomes this by using pulses of light rather than one single flash of light from the time the shutter opens until it closes. The problem is that most studio strobes can only dump their capacitors all at once, and not pulse the light like an HSS speedlight can do, so the question is: How do we get the strobe to fire as the shutter starts moving, no matter the shutter speed? The answer is by using the HSS signal from your camera to fire your strobe, either with an HSS radio trigger and HSS strobe, or by firing your non-HSS strobe optically with an HSS speedlight on the camera.
First, I'll go through the steps I had to use to make this work with my equipment, then we'll look at some of the technical limitations of using hypersync in this way. I use a Canon 60D, Alien Bee B800, and a Yongnuo YN-568EX II, which is an HSS compatible flash. The Alien Bee strobes have a built in optical slave, so an external optical slave trigger (such as a Wein peanut) is not needed in my case. If your strobe does not have a built in optical trigger, you will need an external one. First thing is to set your speedlight in the hotshoe of the camera. Make sure your speedlight is set to HSS.
Turn the flash compensation or manual power down so the speedlight is not adding light to the scene, and point the flash head directly at the optical trigger if shooting outdoors. Inside, the optical slave of the strobe usually has no problem seeing the flash. Depending on if your camera fires a pre-flash or not, you might have to press the Flash Exposure Lock (FEL or *) button prior to pressing the shutter button. Pressing this button will discharge the speedlight and strobe, so make sure the strobe recharges before pressing the shutter button. I found that I could avoid the pre-flash by setting my camera to fire the strobe with manual settings rather than using ETTL by going into Flash Control > External flash func. setting > Flash mode > Manual Flash, then setting the flash output to the lowest setting. A higher power setting on your speedlight might be needed when shooting in direct sunlight.
In the example above, notice that I used a shutter speed of 1/1000, which would be impossible without hypersyncing my strobes.
I have successfully used this method photographing a bridal party on a lake at high noon, so it can be used outdoors in bright light. It wasn't 100% consistent, but it worked well enough for a few quick shots. I do know that this method may not work with every camera/flash combination, so you'll have to test it out for yourself. One thing to keep in mind is the B800 has a flash duration of 1/1100 of a second at full power, or longer at lower power settings, so any shutter speed faster than that will drop the amount of light captured from the strobe in the same way as continuous light (double the shutter speed = -1 stop). I would suggest going through the technical specs of your strobes and finding the flash duration at different power levels as they can vary wildly from on model to another. Another issue is a thin dark band near one of the edges at a shutter speed faster than 1/1000, so be prepared to crop if needed. Obviously, a dedicated HSS strobe and trigger system will work better, but this method works just fine in a pinch.
So what do you gain from hypersyncing your strobe? You gain the ability to shoot at larger apertures since you now have more control over the ambient light by using your shutter speed. It also gives you a better chance at completely stopping fast motion since you can shoot with as fast as a shutter speed as you want. Get out there and try using hypersync in different situations to see what works best for you