Exposure Triangle Calculator (Equivalent Exposures)

They're powers of √2: light transmitted scales with aperture AREA, area scales with diameter squared, so doubling light needs the diameter (and the f-number that encodes it) to grow by √2 ≈ 1.414. The familiar sequence is just √2ⁿ rounded: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 — each step exactly one stop. Third-stop clicks on your dial multiply by 2^(1/6) ≈ 1.12, which is why f/2.8→f/3.2→f/3.5→f/4 takes three clicks.

Exposure Value collapses aperture and shutter into one brightness number: EV = log₂(N²/t), with EV 0 defined as f/1 for 1 second. Bright sun is EV 15 (the Sunny-16 rule restated: f/16, 1/100, ISO 100), overcast 12–13, bright interiors 7–8, city streets at night 4–6, moonlight −2, starlight −6. Knowing the scene's EV turns this calculator into a planning tool: every (N, t, ISO) triple summing to that EV is an equivalent exposure — the creative choice is which one.

No — and the modern phrasing matters: aperture and shutter set how many photons arrive; ISO sets amplification of the signal afterward. Noise is mostly photon statistics, so the cleanest file always comes from maximizing actual light first (aperture, shutter) and using ISO to brighten what remains. On today's near-ISO-invariant sensors, ISO 6400 in-camera and ISO 800 pushed 3 stops in software look similar. The triangle still balances exposure brightness perfectly — just remember one corner is amplification, not photons.

As fourth and fifth currencies in the same stop economy: an ND filter subtracts stops of light (ND8 = −3 stops — this tool's sibling ND calculator extends shutters by exactly that factor); flash adds a fixed packet of light whose reach follows guide-number ÷ f-stop (the inverse-square corner of our flash calculator). Both convert to stops, both balance against the triangle's three sides. The whole craft of exposure is one ledger: stops in, stops out.