Exposure triangle

Reference and replacement are settings for the same scene. Ideal image brightness is proportional to ISO × time / f-number². Positive change means brighter, negative darker; +1 EV doubles it, −1 EV halves it. Raising ISO does not increase the light reaching the sensor.

Time uses seconds: 1/125, 0.008 or 2. Comma, decimal point and scientific notation work; only a single numeric fraction, no expression. Match using selects the replacement value to solve, keeping its other two values unchanged. The selected field may be blank. ISO 200, f/4, 1/250 s → ISO 400, f/4, 1/500 s has equal brightness.

EV = log₂(N²/t) describes aperture and time; EV100 = EV − log₂(ISO/100) normalizes to ISO 100. Additional values can be expanded and are not measured scene brightness. Rounded camera apertures such as f/2.8 to f/4 are not exactly one stop mathematically. Matching rounds to six significant figures; differences below 0.0001 EV count as equal.

Equal ideal brightness does not mean equal quality: time affects motion blur, aperture depth of field/diffraction and ISO noise/dynamic range. No light meter, camera profile, flash or ND model. ISO 1–204800, aperture 0.7–128, time 1/32000–86400 s. Out-of-range matches are reported, not silently clamped. Settings persist during navigation.