Rear curtain flash combined with a slow pan gives you two exposures in one frame: a streaked background from the ambient light, and a sharp subject from the flash at the end of the exposure. The technique is old, but it still produces striking results at night events, car meets, and street races. This article explains the timing, the flash power, and the shutter settings, along with the venue rules to check before you bring a flash.
Why Rear Curtain Sync Matters
With front curtain sync, the flash fires at the start of the exposure, and the ambient streak appears in front of the subject, which looks wrong to most viewers. Rear curtain sync fires the flash at the end, so the streak trails behind the subject as expected. That single setting is what makes the effect read as motion rather than confusion. Check the flash menu for the sync option before you start panning.
The camera’s sync speed also limits the shutter. Most setups need a slower shutter than the fastest speed for flash, so the background has time to streak while the flash does its work. The flash sync speed guide explains that limit in detail.
Set the Shutter and Ambient Exposure First
Pick a slow shutter for the background streak, usually somewhere between one fifteenth and one sixtieth of a second for a moderate pace. Then set the aperture and ISO so the ambient background is about right without any flash. A background that is too dark at this stage will not be rescued by flash, so check the frame before you add light.
Use manual mode for this technique so flash power does not change the shutter. The ambient exposure then acts as a fixed reference, and you can adjust the flash power in small steps until the subject looks right against it.
Dial In the Flash Power Gradually
Start with the flash at low power. Fire a test frame with a stationary subject, then adjust. The aim is a subject lit enough to look sharp, with a background that still streaks. Too much flash flattens the scene and kills the motion, while too little leaves the subject underexposed. Change one step at a time, because small moves make a large difference.
Confirm that the flash fires at the right moment. A flash that fires early places the sharp image in the wrong spot, and one that fires late may miss the subject entirely. Test the trigger with a few passes before you depend on it during the event.
Time the Pan and the Flash Together
Start panning before the subject reaches the frame, and keep the pan going after the flash fires. The flash freezes the subject, but the pan still has to match the speed. Aim to fire when the subject is near the middle of the frame, where you have the most control over the composition. If the subject crosses at an angle, adjust your position so the path runs through the middle.
Some cameras offer a slow sync option that balances flash and ambient light. It can help the background, but it changes the timing, so test it before the event instead of relying on it in the moment.
Check the Venue Rules First
Flash is restricted at many venues, including sports events, theatres, and some night races. Ask the organizers before you bring a flash, and find out whether they allow it at all. Some events forbid any flash because the light can distract athletes or performers. Do not use flash where a rule or a safety notice prohibits it, even if the effect would look good.
- Ask the organizer whether flash is permitted before the day.
- Turn off any AF assist light that could bother the people nearby.
- Keep the flash pointed away from drivers, riders, and officials.
- Carry a spare battery for the flash and a charged camera battery.
- Shoot a test frame before the main event starts.
Use Flash Only Where It Adds Something
The effect works best when the background has detail and the subject is recognizable. Flash can look like a gimmick when the background is dark and empty. Choose scenes with strong background lights, such as a street lit by lamps or a track floodlit at night, where the streaks have something to draw.
Keep the number of flash bursts low. Each flash adds heat and drains the battery, and the frame rate can slow as the flash recycles. Take a few frames at a time, review them, and then reset before the next group.
Frequently Asked Questions
The flash is probably set to front curtain sync. Switch to rear curtain so the flash fires at the end of the exposure, which places the streak behind the moving subject.
Any flash that offers rear curtain sync and manual power will work. Built-in flash often lacks these options, so test your own equipment well before the event.
Start near one fifteenth or one thirtieth of a second. Slower speeds give longer streaks, while faster speeds keep the background cleaner. Adjust after a test frame.
The flash power is too low, the flash points away from the subject, or the subject is beyond the flash’s useful distance. The dark flash photo guide covers the common causes.
The Short Version
Set the flash to rear curtain, use a slow shutter for the background streak, and dial in the flash power in small steps. Pan from before the subject enters the frame and fire the flash near the middle of the frame. Check the venue rules before you bring a flash, and use the technique only where the background has detail.