TYPES OF HIGH-SPEED FLASH PHOTOGRAPHY
There are two technologies that enable high-speed flash photography: High Speed Sync and HyperSync. High Speed Sync, or HSS, refers to shooting with speedlights, while HyperSync involves shooting with larger flash systems.
With HSS photography, speedlight flash photographers can shoot faster than 1/250 sec. If you're a Nikon shooter, this ability is enabled in the custom functions. If you shoot Canon, HSS is activated on the flash unit. When HSS is turned on, the speedlight emits a rapid strobic flash burst during the exposure. This ensures that the scene is always getting flash no matter what the shutter curtains are doing. In essence, it's like illuminating a scene with a continuous beam of light. The flash burst still looks like one pop, but really it's a pulsating beam of light coming out of the flash. Welcome to the flash revolution! Now you can use your speedlight at any speed, and HSS works perfectly with off-camera wireless flash photography.
Larger studio flash systems use a different technology, but with similar results. Unlike TTL (through the lens) speedlights, which use camera data to determine flash exposure, large flash packs simply pop flash at the selected output. You need to use a flash meter or preview your LCD to determine proper exposure. Similar to speedlights, flash clipping will occur if you shoot faster than the camera sync speed. HyperSync changes the game for flash sync with larger flash systems.
PocketWizard designed HyperSync to be used in conjunction with one of its MiniTT1 or FlexTT5 transmitters. With HyperSync enabled, the transmitters recalibrate the timing between the flash pop and shutter curtains. Unlike HSS, which uses a pulsating flash burst, HyperSync uses just one flash burst. HyperSync can time the shutter release during the "flash tail" after the peak flash burst. The tail, although weaker, is a longer duration of light from your flash unit than the peak. This longer duration of light allows you to use incredibly fast shutter speeds.
I use Elinchrom Rangers, and I can shoot at 1/8000 sec. with my Nikon D300S, the maximum shutter speed for most cameras. (I do get a small band of flash clipping in my images at this extreme speed, which is easily cropped out.) In order for HyperSync to work, you need both a PocketWizard transmitter on your camera and a receiver on your flash pack. The latest software version for HyperSync automatically calibrates the specific camera/flash system.
HyperSync performance varies depending on the camera and flash system used. Some photographers may be able to get 1/1000 sec., while others will get 1/2000 sec. or faster. Generally, smaller-sensor cameras work better than larger-sensor cameras. PocketWizard offers sample camera/flash sync speeds on its website (www.pocketwizard.com). Use the slowest flash-duration head your system offers. I use the slower S FreeLite heads with my Elinchrom Rangers and Quadras to get the best performance.
COMPENSATING FOR REDUCED OUTPUTUsing either high-speed flash method will reduce your effective flash range. With one speedlight in HSS mode, I need to be around 6 feet or closer to my subject for the flash to illuminate him. If I fire multiple fast frames, my flash recycling slows down considerably. To remedy this problem, I use multiple flash units, giving me more power and faster recycling.
My Elinchrom Rangers also don't project light as far using HyperSync. I'm not getting the full power of the peak flash burst shooting at super-high speeds. I'll either move my flash closer to the subject or open up my aperture to increase the illumination of my flash. Using a sports reflector on my flash head, I can shoot over 60 feet away at 1/8000 sec. and still hit my subject with flash (using my D300S and an S head), and my Ranger is at about 75% power. I can get more distance at full power.