OM Studio Photography — Studio portrait | omstudiophotography.com
What each move between 0.5 m and 3 m costs in stops, and how to re-meter after a move without clipping highlights.
The inverse square law makes distance predictable: light falls with the square of the distance, so moving a softbox from 1 m to 2 m quarters what reaches the subject — a 2-stop loss. If the head metered f/8 at 1 m, it meters f/4 at 2 m unless power is raised 2 stops.
Taking a 1 m, f/8, ISO 100 setup as the baseline: at 0.5 m the light quadruples, +2 stops, good for f/16; at 1.5 m it drops about 1¼ stops, landing between f/8 and f/5.6; at 2 m it is down 2 stops at f/4; at 3 m it is down about 3¼ stops, wider than f/2.8.
Re-metering procedure after any move: meter at the subject's face before touching the camera. If the reading is within a third of a stop of the target aperture, nudge the power; if it is a full stop or more out, change power in whole steps and re-meter. Adjust aperture last, then check the test frame's histogram for clipped highlights on the forehead and cheekbones.
On narrow screens, swipe or scroll the plate sideways.
Prefer power over aperture when depth of field matters: the 4–5 stops of range on a typical head, down to 1/16 or 1/32, usually absorbs the whole move. Lower power also shortens flash duration — from about 1/300–1/500 s at full power to roughly 1/1,500–1/2,000 s at 1/8 — which helps if the subject moves.
Distance changes softness as well as brightness. A source wraps only when it is at least as large as the subject it covers: a 60 cm box at 1 m wraps a headshot, but half-length at that distance needs 120 cm. Moving a smaller box closer makes it relatively larger — and softer — while gaining stops.
For how distance feeds the three-light build, see the Three-Point Studio Lighting Setup page; for what the fill side should read, see Key-to-Fill Light Ratios for Portraits.
Further reading