Work out aperture f stop instantly with clear inputs, formula shown and shareable results.
Because light passing an aperture depends on its area, one stop changes the f-number by the square root of two, so the new f-number is the old times 2 to the power of stops over two. That square root is why the f-stop sequence runs 1.4, 2, 2.8, 4 rather than doubling, and why closing one stop halves the light rather than the diameter.
Aperture change
new f-number = current f-number x 2 ^ (stops / 2)
Light change
light ratio = 2 ^ (-stops)
new f-number = current f-number x 2 ^ (stops / 2). Because light passing an aperture depends on its area, one stop changes the f-number by the square root of two, so the new f-number is the old times 2 to the power of stops over two.
That square root is why the f-stop sequence runs 1.4, 2, 2.8, 4 rather than doubling, and why closing one stop halves the light rather than the diameter.
Enter current f-number, stops to change. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.