Photography: Flash Sync Speed


Until a few months ago I’d never really used flash much, but it became essential to me as I experimented with different aesthetics in my photography. I don’t want to be in a position where I can’t get the image I want because I don’t have the technical knowledge to achieve it and so I decided to try a series of experiments.

I was curious about the flash sync speed of my Fuji XT2 and what effects I could see if I set a faster shutter speed than the flash sync speed. I experimented with flash and shutter speed combinations to work out the sync speed and to see what sort of manual shutter the camera has.

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 using the EF-X8 flash supplied with the camera.

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

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 really, 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).

Bibliography / Recommended

So far, the best explanation I’ve found about flash is from the course Photography Foundations; Flash, on LinkedIn Learning by Ben Long. I would recommend any of his courses, every one I have seen has been excellent. Although I haven’t actually been taught by every photography teacher ever and so can’t say for sure, I suspect he may be the best photography teacher ever.

*I first published this post on Context and Narrative

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