What is t.5 and t.1 flash duration?

t.5 is the time the flash is above 50% of peak intensity. t.1 is the time above 10% of peak — typically 3x longer than t.5. Manufacturers usually quote t.5 (which sounds faster), but t.1 is more relevant for freezing motion since the tail of the flash curve still contributes to exposure and blur.

How does power level affect flash duration?

Speedlights with IGBT technology get shorter flash durations at lower power (excellent for freezing action at 1/16 or 1/32 power). Studio strobes vary — some get shorter, others longer at reduced power. Check your flash specifications for actual durations at each power level.

What flash duration freezes water splashes?

For sharp water splash images, you need t.5 of 1/5000s (200µs) or faster. Most speedlights achieve this at 1/16 to 1/32 power. Studio strobes vary widely. The technique involves shooting in a dark room and using the flash as the effective shutter speed.

Why does my flash sync speed limit matter?

Flash sync speed (typically 1/200-1/250s) is the fastest shutter speed that works with standard flash. However, for freezing motion with flash, the shutter speed matters less than flash duration — the brief flash pulse is what freezes the subject, not the shutter.

PhotoCalcs

Flash Duration Calculator — Motion Freezing

Estimate flash duration at different power levels to determine motion-freezing capability.

Full Power Duration (t.5)

t.5 at full power in microseconds

Power Reduction

0=1/1, 1=1/2, 2=1/4, 3=1/8...

Flash Type

Affects duration curve

How We Calculate This

Flash duration varies with power level and flash technology:

Speedlight (IGBT)

Duration shortens at lower power. Each stop of power reduction approximately halves the duration (varies by model).

Studio Strobe

Duration behaviour varies by design. Many shorten moderately at lower power.

t.1 vs t.5

t.1 ≈ 3 x t.5 (the actual motion-freezing duration)

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.