Thread: F stops
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Old 17th October 2017
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Re: F stops

The difference in the amount of light admitted (for a given exposure time) for an aperture change of 1 stop is a factor of 2 i.e half or double the amount. That means the surface area of the aperture is also double or half, which is logical: double the surface area and you let in twice the amount of light. Halve the surface area and you admit half the light. If you now do the sums you will see that for the surface area to double or half the diameter will change by a factor of the square root of 2 (1.414).

If you now look at the whole stop changes, give or take a bit, you will see that the aperture diameters change in increments or divisions of 1.414.

i.e. 2.0 x 1.414 ≈ 2.8, 2.8 x 1.414 ≈ 4, 4 x 1.414 ≈ 5.6, 5.6 x 1.414 ≈ 8.0 ....... and so on.

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