What is high speed flash sync and how does it work?

Is there a bit of confusion about high-speed flash sync?

Here are details for you:

What high-speed sync is… when the shutter speed is fast, the shutter does not completely open at once… in fact, there are two curtains to the shutter, the first one followed by a second one…

In normal photography the first curtain opens, and the flash is fired before the second curtain starts to close.

In high-speed shooting, the second curtain is closing before the first curtain has fully opened … So what you have is a slit through which the film or sensor is exposed …

In high-speed sync, the flash strobes multiple times, successively exposing each band of that slit between the two curtains as the slit transits the sensor/film plane …

High speed flash sync is in fact a multiple firing of the flash, in a finely timed synchronized firing of the flash units precisely as the slit transits across the sensor.

This is why it takes expensive smart flash units like the Nikon  SB-800SB-900 and SB-910 to accomplish this technically complex task.

When shooting in high-speed, without high-speed sync, all that one sees in the final image is an exposed slit and bands of black on either side of where the curtain was when shooting.

Sometimes in fact, if you accidentally change your shutter speed while using studio flash, you may get a black band on one side of your image from the shutter not being completely open as the flash fires.

The Nikon  D90 and D7000 are prone to this due to placement of the shutter speed adjustment wheel right under thumb.  Just holding the camera can, and has ruined many shots for me, till I smartened up and now reverse the control direction for the dials… If I now jiggle the dial, I shoot at a slower speed, and do not get the black band in the shot.

Often, one cannot even see this banding in the view finder, particularly when shooting in the dark…

All’s well now, so off you go.

2 thoughts on “What is high speed flash sync and how does it work?”

  1. well I’m thinking of just forgetting the whole hss idea.Can i still capture portraits etc with manual flash triggered flashes with a jcc or simular trigger and will results be good?should i lower shutter speed or increase etc for that?prob start off with oncamera pop up ,with a diffuser,and 1-2 triggered side flashes.any advice for good manual?thanku

    1. Hi Derek,

      Yes. You can shoot a great deal with rigs like those.

      Most studio flash units are used in a format similar to what you describe. And, studio shots are often some of the highest quality, controlled images out there. High speed sync is useful when there is so much (very bright) available light ambiently present requiring short shutter speeds.

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