Practice question · Estimate
By what factor does the light reaching the film fall when the aperture is closed from f/4 to f/8?
Estimate on a scale from no change (1) to a tenth (10).
Hints
- Count the stops first, then convert stops into a factor.
- Each stop is a halving.
Show the answer
4 (answers within ±0.5 count)
Why
By a factor of four. From f/4 to f/8 is two stops, and each stop halves the light, so a quarter arrives. The diameter has halved and the area, which is what actually admits light, has fallen to a quarter, the square relation that the whole f-number series is built on.
Practise Aperture, Shutter and Sensitivity
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