Equivalent Exposure Calculator
The exposure triangle is really one number worn three ways. Aperture, shutter and ISO each change brightness in stops, and a stop is a doubling — so giving one back on one setting to take it on another leaves the picture exactly as bright. What changes is everything else: how blurred the background is, how frozen the movement, how noisy the shadows. That is the whole reason photographers argue about which equivalent to pick.
What this generator does
Picks a base exposure, computes its exposure value at ISO 100, and finds every other combination of full-stop aperture, shutter and ISO settings that produces the same value.
How to use this tool
- Generate a base exposure and read its exposure value.
- Every alternative listed lets in the same light.
- Pick by what else you want: a wider aperture for a blurred background, a faster shutter to freeze movement.
- Note that the listed f-numbers are rounded — the maths accounts for that.
Understanding the controls
- How many alternatives
- Between 3 and 12 equivalent settings to show. Many more usually exist; these are a sample of them.
- Seed
- Any word reproduces exactly the same base exposure and alternatives.
Common use cases
- Choosing settings when you need a particular shutter speed or aperture
- Learning the exposure triangle with real combinations rather than a diagram
- Working out how to keep an exposure while opening up for less depth of field
- Teaching what a stop actually is
- Setting the same exposure problem twice from a seed
How this generator works
Exposure value is logarithmic — it takes the aperture squared over the shutter time, because light gathered goes with the square of the diameter, and subtracts the ISO's own doubling. Two settings are equivalent exactly when those values match. The printed f-numbers are rounded, though: a true stop from f/4 is 5.657, not 5.6, so matching is done to within about a twentieth of a stop. Matching exactly would mean never offering an aperture change at all, which would make the tool useless.
Randomness and fairness
The base exposure is chosen at random; the equivalents follow deterministically from it. A seed reproduces the same problem exactly and is therefore explicitly not cryptographically secure. Without a seed the browser's cryptographically secure generator is used.
For how randomness is produced across the whole site, see how Generate Random works.
Limitations and good to know
- Full stops only. Modern cameras offer third-stop increments, which give many more combinations.
- Exposure value is about brightness alone. It says nothing about how the picture will look, which is the actual reason for choosing between equivalents.
- Real lenses lose a little light at wide apertures, so the marked f-number is not exactly the light transmitted — cinema lenses use T-stops for this reason.
- Reciprocity fails at very long exposures on film, where doubling the time no longer doubles the exposure.
- Exposures are not stored between visits; seed one you want again.
Privacy and your data
Every calculation runs in your browser. Nothing about the exposure or your seed is transmitted or kept.
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