Photo EV from ISO Aperture Time
Computes exposure value EV from a combination of ISO, f-number and exposure time using EV100 = log2(f2/t) - log2(ISO/100).
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EV from ISO, aperture and shutter speed
Exposure Value (EV) rolls the three exposure variables into one number. You get it from EV = log₂(N²/t) − log₂(ISO/100), where N is the f-number, t the shutter time in seconds and ISO the sensor sensitivity. Add +1 EV and you double the light hitting the sensor; −1 EV cuts it in half. Here's a handy anchor. The Sunny 16 rule says ISO 100 + f/16 + 1/100 s gives you EV 15, roughly direct sun at noon. At the other end, EV 0 is ISO 100, f/1.0 and 1 s, the kind of scene you'd shoot under moonlight. Because the stops on aperture (f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16), shutter (1/30, 1/60, 1/125, 1/250…) and ISO (100, 200, 400, 800…) are each 1 EV apart, swapping one for another leaves the exposure where it was.
Applications
Wrapping your head around the exposure triangle, practicing manual-mode shooting, sanity-checking what a handheld light-meter or external app tells you, dialing in exposure compensation for awkward scenes like snow or backlight, showing beginners how to read the in-camera meter, and getting two cameras with different sensors to expose the same way.
FAQ
What does negative EV mean? It's a scene darker than ISO 100 + f/1.0 + 1 s. Shooting the Milky Way puts you around EV −4 to −6, while a city street at night lands closer to EV 3–6.
Why does the formula subtract log₂(ISO/100)? EV uses ISO 100 as its baseline. Double the ISO (say 100 → 200) and you've brightened by a stop, so the equivalent scene EV drops by 1 unit.
Is EV the same as "stops"? When you're talking about a change in exposure, more or less yes; "1 stop overexposed" is the same as +1 EV. The pedantic distinction is that EV is the absolute scale and a stop is the unit you move by.
Related Tools
Exposure Time by ISO and Aperture
Calculates a new exposure time in seconds when ISO and f-number change while keeping the same EV as a reference exposure.
ISO Shutter Aperture by EV
Estimates ISO required to keep the same EV after changing aperture or shutter.
F-Stop Time ISO EV
Computes Exposure Value (EV) from aperture, shutter and ISO.
Bulb Exposure ISO Aperture
Estimates bulb exposure time from scene EV with given ISO and aperture.
Maximum Noise Exposure Time
Calculate the maximum daily allowed noise exposure time, T = 8 ÷ 2^((SPL − 85) ÷ 5), from the sound pressure level SPL (dB(A)). The result, in hours, is the maximum exposure duration before reaching a 100% dose under the Brazilian NR-15 (85 dB(A) limit for 8 h, with a 5 dB dose-doubling rate). Every 5 dB above 85 halves the allowed time: 90 dB(A) allows 4 h, 95 dB(A) only 2 h. It is the basis for dose calculation and the planning of rotation and breaks. Enter the sound pressure level.
Equivalent Exposure by ISO (Shutter Speed)
Keeps brightness constant when the sensitivity changes: t2 = t1 × (ISO1/ISO2), so 1/125s at ISO 400 becomes about 1/31s at ISO 100.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.