Flash Duration Calculator — Motion Freezing

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.

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.

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.

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.