Exposure Triangle Calculator
Calculate the relationship between aperture (f-stop), shutter speed, and ISO. Solve for any one value given the other two, or find the equivalent exposure when changing one setting.
Solve for Unknown Value
Enter any two values to solve for the third (leave one blank).
Equivalent Exposure Calculator
Change one setting and find the equivalent value for another to maintain the same exposure.
Formulas
Exposure Value (EV) at ISO 100:
EV₁₀₀ = log₂(N² / t)
where N = f-number (aperture), t = shutter speed in seconds
EV at any ISO:
EV = log₂(N² / t) − log₂(ISO / 100)
Exposure (luminous exposure H):
H = (t × ISO) / (N² × C)
where C = 250 (ISO 2720 standard calibration constant for reflected-light meters)
Equivalent Exposure (same H):
t₁ × ISO₁ / N₁² = t₂ × ISO₂ / N₂²
Solve for any unknown: N₂ = √(t₂ × ISO₂ × N₁² / (t₁ × ISO₁))
t₂ = t₁ × ISO₁ × N₂² / (ISO₂ × N₁²)
ISO₂ = ISO₁ × t₁ × N₂² / (t₂ × N₁²)
Stops difference:
Aperture stops = 2 × log₂(N₂ / N₁)
Shutter stops = log₂(t₂ / t₁)
ISO stops = log₂(ISO₂ / ISO₁)
Assumptions & References
- Calibration constant C = 250 per ISO 2720:1974 (General Purpose Photographic Exposure Meters).
- EV is defined for ISO 100 as the standard reference per APEX (Additive system of Photographic EXposure).
- Standard aperture series follows the ½-stop and ⅓-stop progressions (f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22…).
- Standard shutter speed series follows the ½-stop and ⅓-stop progressions (1/8000, 1/4000, 1/2000, 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1s…).
- Reference: Peterson, B. (2004). Understanding Exposure. Amphoto Books.
- Reference: Ray, S.F. (2000). Camera Systems. Focal Press.