A stop is a doubling or a halving.
One stop more light is twice the light. Two stops more is four times. One stop less is half, and two stops less is one quarter. Stops are logarithmic, so a change of s stops corresponds to a multiplier of 2^s.
In a manual flash mode whose fractional output corresponds to proportional energy, 1/16 to 1/8 is one stop more, and 1/16 to 1/4 is two stops more. The convention is useful, but it does not mean that 1/16 on an AD100 delivers the same light as 1/16 on an AD600. Head design, modifier, operating mode, distance and captured pulse all matter.
Four ways to change an exposure.
| Goal | Example for +1 stop | Trade-off |
|---|---|---|
| Increase manual flash | 1/16 → 1/8 | Recycle, duration and output headroom |
| Open aperture | f/8 → f/5.6 | Depth of field; flash and ambient brighten |
| Increase ISO | ISO 100 → 200 | Rendering/noise; flash and ambient brighten |
| Move a point source closer | 8 ft → about 5.66 ft | Coverage, shadows, softness and falloff change |
A faster shutter reduces ambient exposure, but its effect on flash depends on the capture mode. Do not apply the “shutter only changes ambient” shortcut to HSS or a global-shutter exposure that clips the pulse.
From the reading to the power change.
If the flash meters f/5.6 and your target camera aperture is f/8, you need approximately one stop more illumination. From 1/16 power, a proportional-output starting estimate is 1/8. You are asking for enough extra light to compensate for closing the aperture; the final photograph should maintain the intended brightness.
If your reference is already at full power, the calculated increase is unavailable. A useful tool must say so. Consider moving the light, opening aperture, increasing ISO, changing the modifier, or using more light. Each option affects the photograph differently. The flash power calculator shows the stop requirement and constraints.
YOUR NEXT 10 MINUTES
Predict. Measure. Refine.
Starting at 1/8, where will a two-stop reduction put the power setting?
Set 1/32. Meter both outputs at the same distance after full recycle.
The prediction is one quarter of the illumination. On a full-stop aperture scale, f/8 would become f/4.
If your measurement differs, inspect the mode, recycle, ambient contamination and pulse capture before applying a correction.