Understanding High-Speed Sync and Flash Timing

Flash synchronization is a crucial concept for anyone working with artificial light. Here's what you need to know.

Coming to you from Karl Taylor with Visual Education, this informative video explores the intricacies of flash synchronization. Traditional shutters in digital cameras function like elevator doors, opening and closing to let in light. The duration for which these doors stay open determines the amount of light that hits the camera's sensor. A longer exposure can result in motion blur, while a quicker one can freeze action. The challenge with flash sync lies in timing the shutter with the burst of flash, especially at higher shutter speeds.

Most digital cameras have a maximum flash sync speed of around 1/250th of a second. Beyond this speed, the shutter mechanism, which operates like a slit scanning across the sensor, struggles to sync with the flash. This can result in partial exposure, where parts of the image are underexposed because the shutter blocks the flash. Leaf shutters, found in more expensive medium format lenses, can sync with flash at much higher speeds. Their design allows for full exposure at any shutter speed, making them ideal for outdoor fashion shoots where daylight needs to be controlled.

High-speed sync (HSS) technology offers a solution for 35mm cameras. By extending the duration of the flash burst to match the shutter's scanning movement, HSS allows for effective flash synchronization at higher speeds. However, this method reduces the flash's power, as only part of the sensor is exposed to light at any given moment. This often requires compensatory adjustments, such as widening the aperture, which can impact the depth of field.

Taylor discusses a significant technological advancement: the global shutter. Unlike traditional or electronic shutters that expose parts of the sensor sequentially, a global shutter exposes the entire sensor simultaneously. This eliminates the issues of banding and partial exposure, allowing for perfect flash sync at any speed. The Sony a9 III, for instance, uses a global shutter, enabling shutter speeds up to 1/80,000th of a second without compromising flash synchronization.

That's just the beginning, though, so check out the video above for the full rundown from Taylor.

If you would like to continue learning about how to light a portrait, be sure to check out "Illuminating The Face: Lighting for Headshots and Portraits With Peter Hurley!"

Alex Cooke's picture

Alex Cooke is a Cleveland-based portrait, events, and landscape photographer. He holds an M.S. in Applied Mathematics and a doctorate in Music Composition. He is also an avid equestrian.

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never needed a sync seed faster than 1/250. Plop on an ND filter and it's not even an issue.

Buy Hasselblad and you able to go all the way up to 1/4000...

Could you explain to me how an ND filter allows you to increase sync speed?

its doesnt. it allows less light to enter your lens, thus reducing your stops. So you can "max" your sync speed at 1/250 and get proper exposure. HSS is usually for when it's too bright outside, or I guess, when you really want to freeze super high speed motion with flash. However I never need shutter speeds beyond 1/250 for my kind of work