Equivalent Exposure Calculator

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

1. Generate a base exposure and read its exposure value.
2. Every alternative listed lets in the same light.
3. Pick by what else you want: a wider aperture for a blurred background, a faster shutter to freeze movement.
4. Note that the listed f-numbers are rounded — the maths accounts for that.

Understanding the controls

How many alternatives

Up to 12 equivalent settings to show (minimum 3). Where more exist these are a sample; one base, f/16 at 1/500 and ISO 100, has only nine.

Seed

Any word reproduces the same base exposure and alternatives for as long as this tool is unchanged.

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 numbers are rounded, though: a true stop from f/8 is f/11.31, not f/11, and the stop after 1/30 is 1/64, not 1/60. So matching is done to within about a sixth of a stop, which takes in every setting the same number of stops from the base and nothing a whole stop out. Matching exactly would rule out every odd stop — f/2.8, f/5.6, f/11 — and leave only the two-stop jumps.

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. Neither the exposure nor your seed is transmitted or kept; what is measured is that the tool was used and how many alternatives were asked for.