ISO Reciprocity
Find the stops gained when changing ISO and the matching shutter speed.
About ISO Reciprocity
Doubling ISO adds one stop of sensitivity, which can be spent on a faster shutter or a smaller aperture while keeping exposure constant. ISO is the exposure control you raise when you run out of shutter speed or aperture, though it adds image noise.
Formula
ISO Reciprocity
Stops = log2(target ISO / current ISO)
- stops gained
- Each stop doubles sensitivity
Worked example
With the default values below, ISO Reciprocity returns ISO Stops Gained of 2.00. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Current ISOminimum 25
- 100
- Target ISOminimum 25
- 400
- Base shutter (1/x s)minimum 1
- 125
Results
- ISO Stops Gained
- 2.00
- Matching Shutter (1/x s)
- 500
- How to Use
- Higher ISO lets you use a faster shutter or smaller aperture
Step by step
- 1Values used
- 2ISO Reciprocity
- 3ISO Stops Gained= 2.00
- 4Matching Shutter (1/x s)= 500
- 5How to Use= Higher ISO lets you use a faster shutter or smaller aperture
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is ISO Reciprocity calculated?
Stops = log2(target ISO / current ISO) Doubling ISO adds one stop of sensitivity, which can be spent on a faster shutter or a smaller aperture while keeping exposure constant.
Why does ISO Reciprocity matter?
ISO is the exposure control you raise when you run out of shutter speed or aperture, though it adds image noise.
What values do I need to enter?
This calculator takes 3 inputs: Current ISO, Target ISO, Base shutter (1/x s). The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.