What is High-Speed Sync? High-Speed Sync allows photographers the ability to shoot using flash at higher than normal flash sync speeds. With older cameras your highest shutter speed that you could flash sync with was either 1/60s or 1/125s. But thanks to the new technology in current digital cameras we are now able to sync at shutter speeds up to 1/8000s of a second.
A few basics about flash:
1. Flash Duration. The amount of time that it takes your flash to dispense it’s set power. A flash set at 1/1(full)-power takes a longer amount of time to discharge than a flash set to, lets say a 1/16-power. Keeping that in mind, if you are going for speed with your shutter, then open up that aperture to let in that smaller about of flash power. (You’re flash will love you for it and so will your batteries)
2. Controlling the Power. The power that is expelled from the flash can be controlled by you the photographer, your camera, or your flash. With flashes in manual mode, the photographer dials in the amount of power. Some cameras have a sensors that meter the “whole scene” and then tell the flashes what power to fire at. The last type is the flashes surveying the scene and dialing in their own power setting from a series of “monitor pre-flashes” that reflect back. Most of the digital cameras made today include some type of through-the-lens (TTL) flash metering. (Nikon – i-TTL, Canon e-TTL)
3. Sync Speed. Flash Sync Speed is the fastest shutter speed that your camera can shoot at without clipping the frame with your shutter. (Or “screwing-up” and using it to your advantage) Most digital SLR cameras sync at 1/250s. Anything over 1/320s is considered high-speed-sync, generally. On a side note, some digital point and shoots have a sync speed of 1/1000s due to their digital shutter system. Check out strobist for an article on that.
4. How Exactly Does High-Speed Snyc Work? When using high-speed sync you must be using dedicated flashes. Your camera and flash are having a very serious conversation one could say, they have to know exactly what one-another are saying. To start things off, make sure that your camera and flashes are compatible for high-speed sync and enable it on all units. Most of the time this only has to be done in the camera.
Lets quickly take a moment to understand what happens with standard sync: Mainly, the shutter must be fully open for the flash to fire (“1st-curtain sync”, “front curtain” – it is also referred to as) or when shooting in rear-sync (or “2nd-curtain sync”) the flash fires at the very last millisecond before the shutter closes.
Going back to high-speed sync; Instead of the flash firing out one giant pulse of light, high-speed sync actually changes the way that the camera tells the flash to fire. The flash now sends out a series of super-fast, low-power flashes. (Don’t mix this up with RPT mode, but the concept is the same.) This light appears to be continuous within the camera and as the shutter curtain is passing over the sensor, the flash also appears to be “on”. Pretty sweet technology when you think about it!
(For Nikon users – Auto FP High Speed Sync is a flash mode used for fill-flash photography under brightly lit conditions. It will fill in and open up shadowed areas in order to portray the greatest detail in subjects. It’s also ideal when using wide aperture lenses, and because it allows fast shutter speeds—up to fastest shutter speeds on compatible Nikon D-SLRs—it is often used for action-stopping sports photography. And for portraits, you can open up your lenses to their full aperture in order to isolate your subject against a blurred background without overexposing the image.
When Auto FP High Speed Sync is selected, the flash will fire for the duration of the shutter curtain’s travel, thus syncing with the camera’s shutter speed when that speed is set higher than the camera’s normal sync speed. Source)
Here is a diagram that displays the difference between normal sync and high-speed sync.
5. The high-speed sync advantage. Now you can use just about any shutter speed with your flash. The disadvantage of doing so is that your flash output is greatly reduced. I have found that the fix for the loss in power is to stack up multiple speedlights to compensate. One other thing that high-speed sync allows you to do is to open-up that aperture in the bright sun and crank that shutter speed higher.
So now that you have a better understanding about high-speed sync watch it in action with Joe McNally in the desert.