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About this tool
Get manual aperture and shutter settings from the lighting condition and ISO using the Sunny 16 rule and the EV = log2(N²/t) formula.
Sunny 16 Exposure Helper converts a described lighting condition and an ISO into a working aperture and shutter speed using the APEX definition EV = log2(N²/t), with EV shifted for sensitivity by log2(ISO/100). Bright sun sits at EV 15 for ISO 100, and each softer condition on the list is exactly one stop down from the one above it. It is aimed at film shooters, fully manual cameras and anyone whose meter has failed mid-shoot.
Open Sunny 16 Exposure Helper on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Values come from EV = log2(N²/t), not a memorised chart, so any ISO and aperture works.
You see both the exact figure and the nearest dial position, plus how far apart they are.
Swap depth of field for motion blur without changing overall brightness.
On a clear, sunny day set the aperture to f/16 and the shutter to roughly 1 divided by the ISO. At ISO 100 that is f/16 at about 1/125 s, which is EV 15 — the exact figure is 1/128 s, and 1/125 is the nearest marked speed.
Open up one stop per step of softer light while keeping the 1/ISO shutter: f/11 in slight overcast, f/8 in full overcast, f/5.6 in heavy overcast with no shadows, and f/4 in open shade. Each step is one stop, which is 1 EV.
Each doubling of ISO adds one EV, so it buys you one stop — either a faster shutter or a smaller aperture. In bright sun at f/16, ISO 100 wants about 1/125 s while ISO 400 wants about 1/500 s.
Yes, because it describes the light rather than the medium. Digital sensors have less highlight headroom than colour negative film, so many photographers expose a third to two thirds of a stop under the Sunny 16 value and check the histogram.
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