Flash Sync Speed Optimizer — Flash Exposure Calculator

Flash sync speed is the fastest shutter speed at which your camera can fully expose the sensor during a single flash burst. Typical values are 1/160 to 1/250 s. Using a faster shutter speed requires High Speed Sync (HSS), which reduces effective flash power.

High Speed Sync lets you use flash above the sync speed by rapidly pulsing it for the duration of the exposure. The tradeoff is lost flash power — roughly one stop for every stop of shutter speed above sync, so about 2-3 stops by 1/1000 s. Use HSS when you need a wide aperture in bright conditions (e.g. outdoor portraits at f/1.4).

Each halving of flash power reduces the guide number by a factor of about 0.71 (one stop). Full-power GN 58 becomes GN 41 at 1/2, GN 29 at 1/4, and so on. Working distance range is directly proportional to the guide number.

Softboxes typically lose 1-2 stops, umbrellas lose 1-1.5 stops, and grids lose 0.5-1 stop. Always account for modifier loss when calculating flash exposure — each stop of loss divides the guide number by √2.