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About this tool
Learn how aperture, shutter speed, and ISO interact with live exposure feedback and scene presets.
The Exposure Triangle Guide computes the exposure value of any aperture, shutter and ISO combination using the standard formula EV100 = log2(N² ÷ t), then subtracts log2(ISO ÷ 100) and adds your metering bias to give the adjusted EV. Alongside the number it reads out what each setting is doing to the picture — depth of field, motion rendering, noise, handheld blur risk and whether your shutter is fast enough for the subject — so you can see why a change to one leg of the triangle forces a change in another. Five scene presets, from Bright Sun at f/8, 1/500, ISO 100 to Indoor Portrait at f/2, 1/125, ISO 800, give you a working starting point.
Open Exposure Triangle Guide on AltFTool — it loads instantly in your browser.
Choose a "Scene Preset" such as Bright Sun or Indoor Portrait, then set "Aperture (f)", "Shutter Speed" and "ISO".
Enter "Focal Length (mm)", "Stabilization", "Meter Bias (EV)" and "Subject Speed" so the reciprocal-rule and freeze checks apply to your shot.
Read the Exposure Status, Adjusted EV, Handheld Risk and Noise Profile cards, then use "Copy Camera Setup" for text or "Export JSON" for the full analysis.
Values come from log2(N²/t) with ISO and exposure-compensation terms applied, so two different settings that share an EV really are equivalent exposures.
Handheld risk uses the reciprocal rule against your focal length, and subject freeze is judged against the speed of what you are photographing.
Copy the whole setup — aperture, shutter, ISO, adjusted EV and verdicts — as text, or export the full analysis as JSON to keep with the shoot notes.
EV100 = log2(aperture² ÷ shutter time in seconds) — so f/8 at 1/500 is log2(64 × 500) = EV 15. Raising ISO lowers the adjusted EV by log2(ISO ÷ 100), which is one stop per doubling: ISO 400 sits two stops below ISO 100.
At least 1 over your focal length — 1/50 s on a 50 mm lens, 1/200 s on a 200 mm. The tool flags handheld risk as High when you are slower than that with stabilisation off, and Moderate when stabilisation is on, because stabilisation buys back stops but does not remove the limit.
The thresholds used here are 1/60 for a still subject, 1/160 for someone walking, 1/500 for sports and 1/1000 for fast action. Anything slower than the threshold for your subject is reported as weak freeze, regardless of how good the exposure looks.
It shifts the adjusted EV by the amount you choose, in third-stop increments from -1 to +1 EV, exactly like exposure compensation on a camera. Positive values brighten the result for backlit or snowy scenes; negative values protect highlights.