OM Studio Photography — Studio portrait

Where the key, fill and hair lights go

Key at 45° and 1.5 m, fill on the camera axis, hair light a full head above the subject — position first, power second.

The key light does the modelling. A 90 cm softbox 1.5 m from the subject, about 45° off the camera axis and a little above eye level, is the standard starting point; with one 400–600 Ws head it typically meters f/8–f/11 at ISO 100. Move the key, not the camera settings, when the face needs a different shape.

The fill sits close to the lens axis so it brightens shadows without drawing a second set of its own. It is not there to light the face — only to hold the shadow side a chosen number of stops below the key, which is what a lighting ratio actually is.

The hair light goes behind the subject and high, a full head above the crown. Rooms with 2.4–2.7 m ceilings give it the height it needs; below 2.4 m it is forced too close and burns a hotspot into the top of the head instead of edging it.

Ratios: how much weaker the fill should be

The ratio is a stop difference: 2:1 is 1 stop, 3:1 about 1.6 stops, 4:1 is 2 stops, 8:1 is 3 stops.

Meter the key side of the face, then the fill side, and count the stops between them. One stop of difference reads as 2:1 — the soft, even look used for commercial and beauty work. About 1.6 stops reads as 3:1, the classic portrait ratio with visible but open shadows.

Two stops gives 4:1, where the shadow side goes clearly dark and the face gains drama; three stops gives 8:1, the low-key look where the fill side nearly disappears. Because most heads offer 4–5 stops of power range down to 1/16 or 1/32, any of these ratios can be dialled in with the power knob rather than by dragging stands.

The full table, with the fill setting needed for each ratio, is on the Key-to-Fill Light Ratios for Portraits page.

2:1 — 1 stop — soft commercial look
3:1 — about 1.6 stops — classic portrait
4:1 — 2 stops — dramatic
8:1 — 3 stops — low key

Soft light needs a source at least as large as the subject it covers: a 60 cm box wraps a headshot at 1 m, but a half-length portrait needs 120 cm at the same distance.

Lower power freezes movement better — a 400–600 Ws head runs about 1/300–1/500 s at full power but 1/1,500–1/2,000 s at 1/8.

The build in three parts

Turning a distance into an aperture

Move the softbox from 1 m to 2 m and the light falls to a quarter — 2 stops — so f/8 must open to f/4.

Light obeys the inverse square law: double the distance and the subject receives a quarter of the light. In exposure terms every doubling costs 2 stops, so a head metered at f/8 from 1 m needs f/4 from 2 m, or a 2-stop power increase, to hold the same exposure.

Halving the distance does the reverse: bring the box in to 0.5 m and the light quadruples, buying 2 stops you can close down for depth of field. The full 0.5–3 m chart, with a re-metering procedure for moving a light without clipping highlights, is on the Softbox Distance and Aperture Chart page.

Distance also changes quality, not just quantity. A source wraps softly only when it is at least as large as the subject it covers: a 60 cm softbox at 1 m wraps a headshot, while a half-length portrait at the same distance needs a 120 cm box.

Camera settings that repeat

ISO 100, f/8–f/11, shutter at or below 1/160–1/250 s, white balance at 5,500–5,600 K — and leave them there.

The shutter's only job in a flash studio is to keep ambient light out, so set it at or under the X-sync limit of 1/160–1/250 s and forget it. Going faster does not darken the flash; it clips the frame with a black band.

White balance goes on the flash, which burns at 5,500–5,600 K — close to midday sun. The tungsten modelling lamp sits near 3,000–3,200 K and is only a preview of the pattern; if the camera is balanced to it, the flash-lit skin goes blue.

Freezing movement is the flash's job, and lower power freezes better: a 400–600 Ws head lasts about 1/300–1/500 s at full power but roughly 1/1,500–1/2,000 s at 1/8. On location, a battery pack gives 200–400 full-power pops per charge with recycle times of 0.1–0.9 s depending on the setting.

ISO 100 — fixed
Aperture f/8–f/11 — from the meter
Shutter 1/160–1/250 s — at or under sync
White balance 5,500–5,600 K — flash preset
Strobe power 1/2 down to 1/16 or 1/32 — the exposure knob

The setup in order: five steps, about 30 minutes

From empty room to first test frame in five steps, with the failure each step is there to catch.

Work in this order so each light is metered against the ones already set. The steps assume the reference kit: one 400–600 Ws head per light and a 90 cm softbox on the key.

Step 1 — Background, about 5 minutes. Roll down seamless paper: 1.5 m wide covers a seated headshot, 2.7 m a couple, 3.5 m a standing group. Typical failure: paper too narrow, so its edge creeps into the frame.
Step 2 — Key light, 5–10 minutes. Softbox at 1.5 m, 45° off axis, just above eye level, half power. Typical failure: key parked on the camera axis, which flattens the face.
Step 3 — Fill, about 5 minutes. On the lens axis; meter it 1 stop under the key for 2:1. Typical failure: fill placed off-axis, casting a second shadow that reads as dirt on the face.
Step 4 — Hair light, about 5 minutes. A full head above the crown. Typical failure: a hotspot on the top of the head when the ceiling is under 2.4 m.
Step 5 — Camera and test frame, about 5 minutes. ISO 100, 1/160–1/250 s, white balance 5,500–5,600 K; meter the key for f/8–f/11. Typical failures: a black band from exceeding sync, or blue skin from balancing to the modelling lamp.

A starting exposure you can repeat

Starting settings for one 400–600 Ws head in a 90 cm softbox at 1.5 m, and the range each setting can move through.
Setting	Start here	Working range	What it depends on
Shutter speed	1/125 s	up to 1/160–1/250 s	the camera's X-sync limit
Aperture	f/8	f/4–f/11	light distance and strobe power
ISO	100	keep fixed	repeatability between sessions
Strobe power	1/2 power	full to 1/16 or 1/32	4–5 stops of control range
White balance	5,500–5,600 K	flash preset	the flash, not the 3,000–3,200 K modelling lamp
Flash duration	1/300–1/500 s at full power	to 1/1,500–1/2,000 s at 1/8 power	the power setting in use
Key-to-subject distance	1.5 m	1–3 m	each doubling costs 2 stops

Starting settings for one 400–600 Ws head in a 90 cm softbox at 1.5 m, and the range each setting can move through.

The layout in figures

Diagrams and charts from the sections above, gathered for quick reference at the bench.

The key terms of this guide, drawn to one scale

Where the numbers come from

The numbers reflect the physics of flash exposure and widely published equipment ratings rather than any single maker's manual.