← ToolBox / 曝光值 EV 计算

📣 Exposure Value (EV) Calculator

Calculate the exposure value from aperture and shutter speed, and find equivalent EV combinations for the same brightness.

光圈 f

快门秒

ISO

EV = log₂(N²/t)；EV₁₀₀ = EV − log₂(ISO/100)

同场景 EV 恒定，调整三者需保持平衡。

📚 深度解析：曝光值 EV@ISO100 换算

基准换算

f/5.6、1/250、ISO200：EV@ISO100 = log2(N²/t×100/ISO) = log2(31.36×250×0.5) = log2(3920) ≈ 11.94；等效 ISO100 下 f/5.6·1/500。

补偿理解

EV11.9 加 +1 补偿：等效减一档快门或开一档光圈，画面提亮一倍。

EV 和 EV@ISO100 区别？: EV 含当前 ISO，EV@ISO100 归一到 ISO100 便于横向比较；差 = log2(ISO/100)。
互易律靠谱吗？: 常规曝光成立，但极长/极短曝光有倒易律失效（需补偿），闪光与持续光也不同。

Item	Formula / Rule	Source / Standard
Constant per scene	Within one scene luminance, any pair keeping N²/t constant yields the same EV	ISO 2720:1974 General-purpose photographic exposure meters
Scale relation	Raising EV by one halves the light admitted, and lowering it by one doubles it	ISO 2720:1974 §3 exposure value definition
Metering offset	Against an 18% grey reference, snow needs about +1.5 EV while backlit shots meter for the subject	ISO 2720:1974 Annex A exposure tables