Calculate equivalent exposures with aperture, shutter speed, and ISO adjustments.
Photography Exposure Calculator begins with a known aperture, shutter speed, and ISO combination and balances proposed changes to find an equivalent combination. It expresses each adjustment in stops, then supplies the setting needed to cancel the net gain or loss. The common surprise is that f-numbers are not linear: moving from f/4 to f/8 cuts transmitted light to one quarter, which is two stops rather than one. An equivalent result targets the same nominal brightness, not the same depth of field, motion rendering, noise, or highlight capacity.
A concrete input and expected output from the current implementation.
Input
Starting exposure: f/4, 1/125 s, ISO 100 Adjusted settings: f/8, ISO 400
Expected output
Equivalent shutter speed: 1/125 s
At f/8, the lens admits one quarter as much light as at f/4, a loss of two stops. ISO 400 is two stops above ISO 100, so those changes cancel and the shutter time stays at 1/125 s.
Starting from the reference trio, the calculator compares the requested aperture, shutter, and ISO values in stop units. Doubling ISO contributes one positive stop, doubling shutter time contributes one positive stop, and multiplying the f-number by the square root of 2 removes one stop. It solves for the remaining adjustment that brings the combined change back to zero.
For equivalent metered brightness under unchanged light, the numeric balance is proportional to ISO multiplied by shutter time and divided by the square of the f-number. Combinations with the same value balance mathematically. The result does not simulate the photograph or determine whether a camera or lens offers the calculated setting.
Aperture exposure follows the square of the f-number ratio. A one-stop change multiplies the f-number by about 1.414, giving the familiar f/4, f/5.6, f/8 sequence. Therefore f/4 to f/5.6 is one stop, while f/4 to f/8 is two stops.
No. They can produce the same nominal brightness under unchanged lighting, but aperture changes depth of field and diffraction, shutter speed changes motion blur and camera shake, and ISO can affect noise and highlight headroom. Subject movement, flicker, flash duration, and automatic camera processing can create further differences.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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