闪光导数
Flash 指南编号计算器
FlashGuideNumber
Flash Guide Number Calculator
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Calculate flash exposure using guide numbers for proper fill flash and off-camera flash photography.
Características Principales
Flash guide number explanation and calculation
Distance-to-aperture relationship for correct exposure
GN = aperture × distance formula application
ISO influence on effective guide number
Reduction for bouncing and diffusion
Flash sync speed and shutter speed considerations
How to Use Flash Guide Number
Find Guide Number
Locate your flash's guide number in the manual or specifications
Measure Distance
Determine the distance from flash to subject in meters or feet
Calculate Aperture
Divide guide number by distance to determine required f-stop
Account for ISO
Adjust for different ISO settings; higher ISO increases effective guide number
Consider Modifiers
Reduce guide number when using diffusers or bouncing (typically by 1-2 stops)
Set Camera
Set aperture on camera and use appropriate shutter speed for ambient exposure
Casos de Uso
Flash fill for backlit outdoor portraits
Off-camera flash photography with manual exposure
Event photography with minimal ambient light
Creative flash techniques with bounce and diffusion
Preguntas Frecuentes
What is a guide number?
A number indicating flash power capability at ISO 100. Higher numbers mean more powerful flashes.
How do I calculate aperture from guide number?
Divide GN by distance. For GN 50 and 10 feet distance: 50 ÷ 10 = f/5, use aperture f/5.6.
Does guide number change with ISO?
Effectively yes. At ISO 400, you can use smaller apertures (2 stops) while at ISO 100.
How much does diffusion reduce guide number?
Diffusers typically reduce GN by 1-2 stops. Bouncing may reduce it 2-3 stops depending on surfaces.
What is flash sync speed?
Maximum shutter speed (usually 1/200 to 1/320 second) where camera sync curtains allow full flash exposure.