Open-flash calculator.
Calculate the number of flashes required for the open-flash method – including environment correction for indoor and outdoor work plus setup recommendations based on flash count.
Useful when a single flash isn't enough or you combine several weaker units.
- ◆Inverse-square law
- ◆Indoor / outdoor
- ◆Setup advice
- ◆Sync methods
Open-Flash Calculator: Number of Flashes
Calculate the number of flashes needed for the open-flash method
Input Parameters
Outdoors, the guide number is divided by 1.14 (fewer reflections)
Calculation Basis:
- • Formula: Flash count = (Distance × Aperture ÷ Guide Number)²
- • Inverse square law
- • Outdoor correction: Guide Number ÷ 1.14
- • Rounded up to whole flashes
Calculation Results
What is the open-flash method?
- • Multiple flashes are fired simultaneously
- • Adds light output for greater distances
- • Especially useful for large subjects or distances
- • Flashes must be synchronized
- • Alternative to a single, very strong flash
Understanding the open-flash method.
With the open-flash method, several flash units are fired at the same time to deliver more light. Particularly useful when a single flash isn't enough or isn't available.
Typical use cases.
- Large distances to the subject
- Small apertures for greater depth of field
- Weak flashes as the only available option
- Even lighting of large areas
- Backup system for critical shots
Where the method shines – and where it doesn't.
Pros: higher light output through additive effect, flexibility with weaker existing flashes, better light distribution, built-in redundancy.
Cons: more complex setup and synchronisation, higher cost with many flashes, harder to shape the light, more equipment to transport.
Squared relationship.
Light output follows the inverse-square law – which is why the number of flashes you need grows disproportionately as distance or aperture get bigger.
GN 32 · f/8 · 10 m · indoors
Number of flashes = (10 × 8 ÷ 32)² = (2.5)² = 6.25 ≈ 7 flashes
Outdoors: GN_eff = 32 ÷ 1.14 = 28.1 → (10 × 8 ÷ 28.1)² ≈ 8 flashes
More flashes, more effort.
With every additional flash, synchronisation effort grows. This overview shows where a simple setup will do – and where things turn professional.
| Flash count | Setup type | Complexity | Recommendation |
|---|---|---|---|
| 1 | Single flash is enough | Minimal | Standard flash photography |
| 2 | Basic kit | Easy | Master–slave system |
| 3 – 4 | Standard setup | Medium | Wireless sync recommended |
| 5 – 8 | Advanced setup | High | Professional sync required |
| 9+ | Impractical | Very high | Consider alternative light sources |
Five pointers for open-flash setups.
Three methods compared.
Cable, optical or radio – every method has its strengths. This overview helps you pick the right one for your setup.
Reliable, but limited.
- Sync cable: reliable, limited range
- Y-cable: suitable for 2–3 flashes
- Sync splitter: more flashes via amplifier
No batteries, very reliable – but cables get in the way and limit flexibility.
Affordable, but weather-dependent.
- Slave cells: react to another flash
- TTL pre-flash: often problematic on modern cameras
- Range: depends on ambient light
A very cheap option, but unreliable in bright sun or with other flashes nearby.
Flexible, but pricier.
- Radio triggers: long range, very reliable
- TTL capability: modern systems with automation
- Channels: several groups controlled separately
Recommendation: 2 flashes – cable or optical slave; 3–4 – radio or sync splitter; 5+ – professional radio system.
Answers to common questions.
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Solid photography knowledge.
Calculators give you the number. On the blog and in 1:1 coaching I turn theory into results you can see in your images.