Flash Photography (Godox V1S / iM20)

Fill flash — set the ambient first

Balance flash with ambient so the subject looks natural, not "flashed":

1. Manual (M): dial shutter, aperture and ISO so the background sits about ⅔–1 stop darker than you want the subject — leaving room for the flash to lift them.
2. Keep shutter at or below sync speed (1/200–1/250 s on the a7R III); for faster/wider, switch on HSS.
3. Start the V1S in TTL, then use Flash Exposure Compensation (FEC): −0.7 to −1.3 EV for subtle fill, near 0 EV for a more prominent flash.
4. Soften and angle: bounce card or AK-R1 dome, head 30–45° off-axis, slightly above eye level for catchlights.

Outdoor portrait starting formula: f/2.8 · 1/200 s · ISO 100, sun behind/side of subject for rim light, TTL at −0.7 EV. Enable HSS to shoot wide open (f/1.8) in bright sun; add a ¼ CTO gel at golden hour to match the warm ambient.

Portrait lighting setups (V1S)

Base: Manual, 1/160–1/200 s, ISO 100, White Balance 5600K, single-shot Drive Mode.

• Soft natural (daylight + fill): V1S 45° off-axis, slightly above eye level, small diffuser; power ~1/64–1/32; f/1.4–f/2.8.
• Dramatic low-key: V1S 90° side or slightly behind, no diffuser (or snoot/grid); power 1/16–1/8; f/4 — deep shadows, cinematic.
• Beauty (even): V1S on-axis, ~30° down for butterfly light, softbox; power 1/32–1/16; f/5.6.
• Continuous LED only: flash off, modelling light full, ~30–50 cm with diffuser; f/1.4–f/2, ISO 800–1600, 1/60 s.

Flash modes

HSS (High-Speed Sync) — pulses the flash so it syncs above the camera's native sync speed (~1/160–1/250 s), avoiding the black band. Use for wide apertures or freezing motion in bright light; effective power drops as shutter climbs, so raise ISO or open up.

Wireless (Godox X radio) — on-camera V1S as Master controls other units; off-camera set to Slave and fire via a trigger (XPro-S / X2T-S). Match channel and group across all units. Radio beats Sony's optical wireless for range and no line-of-sight.

Multi / stroboscopic — fires several bursts in one exposure to record phases of motion. Set Hz (flashes per second) and Times (total bursts); e.g. 10 Hz × 5 at 1/16 over a 0.5 s exposure. Works best in a dark/controlled scene.

Slow sync flash ambient + freeze

A slow shutter records the ambient while the flash freezes the subject. Choose Rear Sync (flash at the end of the exposure) so trails follow the movement naturally; Slow Sync (front curtain) puts trails ahead of the subject.

Scenario	Mode	Shutter	Aperture	ISO	Flash	Sync
Night street portrait	M	1/10 s	f/2	200	TTL	Rear
City light trails	M	1/2 s	f/4	100	Manual 1/32	Rear
Indoor ambient + fill	A	~1/15 s	f/2.8	400	TTL	Slow

Start point: 1/15 s, f/2, ISO 200. Tripod or pan; dial flash power down to let the ambient dominate for a cinematic feel.

Modelling light

The V1S's continuous LED (~5600K) previews where highlights, shadows and catchlights will fall, and assists autofocus in low light. Use medium brightness to place shadows, full to check catchlights (aim for the 10 or 2 o'clock position in the eye), low to focus without dazzling. It drains the battery faster and can mismatch tungsten/fluorescent ambient unless gelled.

Off-camera placement

A — direct: flash aimed straight at the subject. B — bounce off ceiling: softer, avoids the on-camera "deer-in-headlights" look. C — bounce + diffuser panel: ceiling bounce fills the room while the panel adds directional light on the subject — the best quality of the three.

Guide number (manual exposure)

V1S GN ≈ 42 m at ISO 100 (105mm zoom, full power). Then:

• Aperture = GN ÷ distance — subject at 10 m → 42 ÷ 10 ≈ f/4.2.
• Distance = GN ÷ aperture — at f/8 → 42 ÷ 8 ≈ 5.25 m.

Changing ISO, flash zoom or adding modifiers alters the effective GN — the V1S shows the calculation on its LCD in Manual.

Godox iM20 (manual mini flash) starting points

Scenario	Mode	Aperture	ISO	Power
Indoor portrait	A / M	f/2.8–f/4	200–800	1/8–1/16
Fill flash (sunny)	A	f/5.6–f/8	100–200	1/16–1/32
Night street	M, 1/60 s	f/2–f/2.8	800–1600	1/8–1/4
Macro / close-up	—	f/8–f/11	200–400	1/8–1/16

Diffuse a small hard flash with baking paper/tissue; a white card angled in front gives a DIY bounce.

Five creative "movement" ideas

Idea	Key settings
Cyclist at night (rear-curtain)	M, 1/15 s, f/5.6, ISO 400, flash ~1/16; meter ambient 1 stop under
Dancer mid-leap (Multi)	1/4 s, f/8, ISO 200, Multi 3–5 × 10 Hz @ 1/32, dark room, off-camera
Water splash (short flash duration)	1/200 s, f/11–f/16, ISO 100, power 1/32–1/64, two diffused flashes at 45°
Runner (panning + fill)	1/30 s, f/5.6, flash 1/8; pan, ambient 1 stop under
Fabric / hair toss (studio)	1/200 s, f/8–f/11, ISO 100, key 1/16 softbox + rim 1/32; fire at the apex

What HSS actually costs

Above the native sync speed (a7R III: 1/250 s; a6400: 1/160 s) the rear curtain begins closing before the front curtain is fully open, so only a moving slit of sensor is exposed. HSS keeps the flash burning for the whole traverse rather than firing one short pop — which means much lower effective output. Budget around 1/2 power for outdoor fill at 1/1000 s, f/2.8, ISO 100, and switch HSS on at both the flash and the trigger.

Fuller treatment of both dragging the shutter and beating it: Slow Sync & High-Speed Sync Flash.

Consolidated from notes: Flash uses; Using my new flash; Flash for portraiture settings; Flash modes; Slow Sync Flash cheat sheat; Slow Sync Flash with godox; Using Godox Flash - modelling light; Placement of attached flash; Godox Flash - Guide number; Flash Photography - Godox iM20; five photographic subject ideas using flash