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03 // Bidirectional STEM Calculators // EVERYDAYEV = log₂((N² / t) × (100 / ISO))

Photography Exposure Value (EV), Aperture, Shutter & ISO Solver

In the additive APEX photographic system, Exposure Value (EV) combines lens aperture f-number N, shutter duration t (in seconds), and sensor sensitivity ISO onto a base-2 logarithmic stop scale.

EV = log₂((N² / t) × (100 / ISO))
Pick which value you want to calculate (or type into any field):Solving for: EV — Exposure Value (EV Stops)
Calculated

Scene luminance exposure value (Sunny 16 = EV 15)

-622
unit

Lens focal ratio (e.g., 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11, 16)

0.9564
unit

Shutter duration in seconds (0.0025 s = 1/400 s)

0.00012560

Arithmetic ISO speed (100, 200, 400, 800, 1600, 3200)

25102,400.00
unit
Calculated Result · Exposure Value (EV Stops) (EV)
14.6439

Step-by-Step Calculation

01Canonical Law: EV = log₂((N² / t) × (100 / ISO))
02Given Inputs (Base Units): N (f/) = 8, t (s) = 0.0025 s, ISO = 100
03Solve for EV (Exposure Value (EV Stops)): EV = 14.6439

In the additive APEX photographic system, Exposure Value (EV) combines lens aperture f-number N, shutter duration t (in seconds), and sensor sensitivity ISO onto a base-2 logarithmic stop scale.

Real-World Reference Values

Sunny 16 Daylight RuleEV 15 (f/16, 1/125s @ ISO 100)

Direct midday sunlight exposure benchmark

Golden Hour / OvercastEV 12 (f/4.0, 1/250s @ ISO 100)

3 stops (8×) less light than full sun

Indoor Ambient / Night StreetEV 5 – EV 7

Requires fast prime aperture (f/1.4–f/2.0) or higher ISO

20-Row Comparison Table

Exposure Value (EV Stops) (EV) · Aperture f-Number (f/N) (N (f/))

Photography Exposure Value (EV), Aperture, Shutter & ISO Solver — Aperture f-Number (f/N) → Exposure Value (EV Stops)
#Aperture f-Number (f/N) (N (f/))Exposure Value (EV Stops) (EV)Δ %
010.95 8.4959 -41.98%
021.7773 10.3033 -29.64%
032.6047 11.4061 -22.11%
043.432 12.202 -16.68%
054.2593 12.8251 -12.42%
065.0867 13.3373 -8.92%
075.914 13.7721 -5.95%
086.7413 14.1499 -3.37%
097.5687 14.4839 -1.09%
108 Current14.6439 0.00%
119.2234 15.0544 +2.80%
1210.0507 15.3023 +4.50%
1310.878 15.5305 +6.06%
1411.7054 15.7421 +7.50%
1512.5327 15.9391 +8.85%
1613.36 16.1236 +10.10%
1714.1874 16.2969 +11.29%
1815.0147 16.4605 +12.41%
1915.842 16.6152 +13.46%
2016.6694 16.7621 +14.47%
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Frequently Asked Questions

Why do full f-stop numbers increase by factors of √2 (1.4, 2.0, 2.8, 4.0, 5.6, 8)?+

Because circular pupil area scales with diameter squared (1 / N²), multiplying f-number N by √2 (≈ 1.414) halves the light area (-1 EV stop).

How do I find the new shutter speed t when stopping down from f/2.8 to f/8 at the same EV?+

Keep EV locked at your scene reading, click SOLVE FOR on t (s), and change N from 2.8 to 8.0.

How do I convert decimal seconds t into a shutter fraction (1/X)?+

Take the reciprocal 1 / t: for t = 0.0025 s, 1 / 0.0025 = 1/400 second.