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4 minute read
How to Use High Speed Sync Flash
Although flash traditionally cannot be used with shutter speeds faster than your camera’s sync speed, the FP flash mode allows this rule to be broken. Here’s how.
Your camera’s sync speed is the fastest shutter speed at which it can synchronise with flash to produce a properly exposed photograph. Go any faster and you risk seeing black bars across the picture where the very brief burst of flash light has not illuminated the sensor properly.
© Michael Bulbenko | High speed sync flash
This can be a problem when using flash outdoors: should you want to restrict depth-of-field by using a large aperture, this can easily push the shutter speed above the 1/180 sec or 1/250 sec sync speed limit of your X Series camera. But there are ways to get past this threshold, so your creativity isn’t curtailed by technological limits.
Before we look at how to do this, however, let’s remind ourselves of how the sync speed limit came about in the first place.
Sync Speed Explained
The origins of sync speed come from the way in which your camera’s focal plane shutter operates. This comprises two metal curtains, the first of which moves out of the way to expose the sensor to light. The second curtain then covers the sensor again to end the exposure. The gap between these two events is the shutter speed. Every camera in the X Series features a focal plane shutter, except for X100 models, which use a leaf shutter.
As we select increasingly faster shutter speeds, the time between the first curtain opening and the second one closing gets less and less, until we reach a point where the second curtain needs to start closing before the first one has opened fully. In this way, the curtains can be thought to be forming a slit that moves across the sensor, exposing it a little bit at a time. The fastest shutter speed where the curtains open fully, and don’t form a moving slit, is the camera’s sync speed.
If we activate a flash during an exposure where the shutter is fully open, the light from the flash illuminates the whole sensor and gives us a complete picture – no problems there. But if we activate a short burst of flash when only part of the shutter is revealed, then only this part of the sensor is illuminated – the rest will be dark and will give rise to the ominous black band we see when using flash at shutter speeds faster than the sync speed.
The Cure for the Sync Speed Blues
Making images with flash at shutter speeds higher than the sync speed is not possible with ordinary flash equipment, but it is with advanced external flashes, which boast FP mode, also known as high speed sync (HSS). This works by strobing the flash very quickly to provide continuous illumination for the time it takes for both curtains to travel across the sensor.
FP mode works very well indeed, allowing shutter speeds right up to 1/8000 sec (depending on camera model) to be used with flash. This opens up lots of creative doors to photographers – not only using wide apertures to restrict depth-of-field, but also underexposing the ambient-lit background in a photo while correctly lighting objects in the foreground with flash. It’s a very powerful effect that lets bold vibrant colours sing out.
But if you want to use automatic or semiautomatic exposure modes, it’s really important to make sure FP mode is switched on both on the flash and your camera. Refer to your flash unit’s manual to check how to switch the mode on. To activate it on your camera:
- Attach and switch on an external flash unit.
- Navigate to the FLASH SETTING menu and select FLASH FUNCTION SETTING.
- In the window that opens, make sure FP is chosen next to SYNC.
© Michael Bulbenko
Now, pick an automatic (P) or semiautomatic mode (A or S) and set exposure compensation on your camera to a negative value, such as -1 or -1.5. This will affect the ambient light exposure (ie the background), but not the flash exposure (ie the foreground), but only works on subjects that are within one to two meters from the camera and flash.
Your Next Steps
- CHALLENGE Grab yourself a flash that can work in FP mode and make some pictures that underexpose the background but correctly expose the foreground, as described above. Post your favourite images to social media with the hashtag #learnwithfujifilm and #flash. You can also submit your work here for a chance to be featured on our social media channels
