What is Flash Sync Speed?

I’m going to show you what flash sync speed is with a little experiment using my Fuji XT2. You can try an experiment like this with any digital camera and it will give you an idea about what type of manual shutter your camera uses, what the sync speed is, and how far you can push it.

The Fuji XT2 has options for manual and electronic shutter use. The shutter speed on the camera dial goes up to 1/8000s which is the fastest manual shutter speed. The electronic shutter goes up to 1/3200s, but I’ll get to that electronic shutter later. For the moment I’m just looking at the manual shutter and not looking at any high speed sync options, etc.

For these images I’m firing the EF-X8 flash supplied with the camera for each shot, leaving the aperture constant and just changing the shutter speed from 1/60s and moving down one stop* each shot, all the way to 1/8000s. The camera is taking care of ISO and flash power settings. It helps to keep the camera on a tripod or somewhere its can’t move so that you can compare the shots properly.

So these first three shots are all okay; perhaps some blown-out highlights, but they are even.

SarahScott516860_can_tech_flash (1 of 8)
1/60 s @ f2.8
SarahScott516860_can_tech_flash (2 of 8)
1/125s @ f2.8
SarahScott516860_can_tech_flash (3 of 8)
1/250s @ f2.8

However, from 1/500s onwards you can see the image progressively darkens from the base…

SarahScott516860_can_tech_flash (4 of 8)
1/500s @ f2.8
SarahScott516860_can_tech_flash (5 of 8)
1/1000s @ f2.8
SarahScott516860_can_tech_flash (6 of 8)
1/2000s @ f2.8
SarahScott516860_can_tech_flash (7 of 8)
1/4000s @ f 2.8
SarahScott516860_can_tech_flash (8 of 8)
1/8000s @ f2.8

So, what’s happening here? Essentially what you can see at speeds higher than 1/250s is the movement of the shutter.

My camera and flash are metering automatically through-the-lens (TTL). So, there’s a pre- flash which is triggered that sends data back to the camera about required flash settings before the shutter is opened and the main flash fires to take the shot.

There are several different types of shutters, but this Fujifilm camera has a focal plane shutter which is like curtains sitting in front of the sensor. Both curtains move, and the sensor is exposed in sections, each part for the same amount of time. At speeds of up to 1/250s, the flash fires when one curtain has fully opened and the other has not yet started to move; the shutter is fully open exposing the entire image sensor. However, at speeds of over 1/250s, the shutter is never fully open. As one curtain is moving up, the other starts moving, exposing the image sensor in sections. The flash fires, but now you can see the effect of the shutter on the image; the flash has been fired when only a small part of the image sensor is exposed. The faster the shutter speed, the worse this effect is. The camera is exposing the image sensor in smaller and smaller sections or slices. You can see from these shots that the Fuji shutter moves down and not from the left or right; it’s a guillotine shutter (the image is upside down on the image sensor so that’s why it looks like it’s running bottom to top).

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