Question 1

How does flash duration affect motion blur?

Accepted Answer

Flash duration refers to the length of time the light burst lasts, which is often much shorter than the camera's physical shutter speed. When capturing fast-moving subjects, the flash duration acts as your 'effective' shutter speed, slicing the exposure time to freeze motion instantaneously.

Even if your shutter is open for a longer duration, the image is only recorded while the flash is firing. By adjusting your flash power settings, you can shorten the duration, allowing you to capture sharp, clear images of subjects moving at high velocities, such as athletes, birds, or liquids.

Question 2

What is the difference between t.1 and t.5 flash duration?

Accepted Answer

The terms t.1 and t.5 are standard metrics used to measure the light output over time. The t.5 measurement indicates the duration from the start of the burst until the light intensity drops to 50% of its peak power, while t.1 measures the duration until the intensity drops to 10% of its peak.

For professional action photography, the t.1 value is the more critical metric. Because the light is still quite strong at the 50% point (t.5), that 'tail' of the flash can still contribute to visible motion blur on the edges of a subject. Relying on t.1 ensures you have a more accurate calculation of when the action is truly frozen.

Question 3

Can I freeze motion without a high-speed sync (HSS) flash?

Accepted Answer

Yes, you can freeze motion without using HSS by utilizing the flash's natural short duration at lower power settings. High-Speed Sync is designed to allow flash at very fast shutter speeds by pulsing the light, which ironically often increases the total flash duration and can actually make freezing fast motion more difficult.

Instead, you can operate in a darker environment using a standard sync speed and lower flash power settings. Lower power settings typically result in a shorter flash duration, making them ideal for freezing movement without needing expensive HSS-capable triggers or cameras.

Question 4

How do I calculate the required flash duration for sports photography?

Accepted Answer

To calculate the required duration, you must consider the subject's speed, the camera-to-subject distance, and the focal length of your lens. Faster subjects or subjects moving across the frame (perpendicular) require a shorter flash duration to remain sharp.

This calculator determines the maximum allowable flash duration by analyzing these variables to ensure that the subject does not move more than an acceptable distance—typically less than a few pixels—during the flash burst. By inputting your specific scene parameters, you can determine if your current strobe settings will effectively freeze the action.

Free Photography Flash Duration Motion Freeze Calculator