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f-ratio
- f-ratio is the ratio of focal length to aperture
- Aperture is defined as the focal length/f-ratio.
- Each f-stop increases brightness twice, or EV by 1.
- One f-stop is an increase by a factor of \(1/\sqrt{2}\)
- A half f-stop is an increase by a factor of \((\frac{1}{\sqrt{2}})^\frac{1}{2}\)