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).

f/0.7 – f/64
e.g. 0.01 for 1/100s, 2 for 2s
1 – 3,280,000

Equivalent Exposure Calculator

Change one setting and find the equivalent value for another to maintain the same exposure.

Fill in two of the three "New" fields to solve for the third.

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…).
  • Standard ISO series: 100, 200, 400, 800, 1600, 3200, 6400, 12800, 25600, 51200…
  • The "f/16 sunny day rule": EV₁₀₀ ≈ 15 for a sunny day with distinct shadows.
  • Depth of field and motion blur assessments are qualitative guidelines, not precise optical calculations.
  • Equivalent exposure assumes the same scene luminance and no vignetting or transmission losses.
  • Reference: Peterson, B. (2004). Understanding Exposure. Amphoto Books.
  • Reference: Ray, S.F. (2000). Camera Systems. Focal Press.

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