F-Stop Calculator
Enter two apertures to find the difference in stops between them and the light ratio. The smaller f-number always lets in more light.
How to use the f-stop calculator
- Enter the first aperture f-number.
- Enter the second aperture f-number.
- Read the stop difference, the light ratio and which aperture is brighter.
Examples
One stop apart
f/2 and f/4
2 stops, f/2 lets in 4x the light
A third of a stop
f/2.8 and f/3.2
0.39 stops, a 1.31x light difference
Frequently asked questions
What is a stop in photography?
A stop is a doubling or halving of light. Opening up one stop doubles the light; closing down one stop halves it. Stops apply to aperture, shutter speed and ISO alike.
How are stops between two f-stops calculated?
Light scales with aperture area, which goes as one over the f-number squared. So the difference is two times the base-2 log of the ratio of the f-numbers.
Why does a bigger f-number mean less light?
The f-number is the focal length divided by the aperture diameter, so a bigger number is a smaller opening. That is why f/16 is much darker than f/2.
What does the light ratio mean?
The light ratio is how many times more light the brighter aperture gathers. Two stops is a 4x ratio, three stops is 8x, and one stop is 2x.
Are the full-stop f-numbers a fixed sequence?
Yes. The full-stop series is f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22 and so on, each step a factor of the square root of two.
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