1. ## F1.8 vs F3.2

Say I take a 1s shot using F1.8. How many seconds would it take for a F3.2 lens to get the same level of exposure? Are there any formula I could use?

2. I'm sure there's a complex mathematical formula somewhere, but use the following table until someone coughs it up:

f1.4
-- f1.6
-- f1.8
f2.0
f2.8
-- f3.2
-- f3.5
f4

Each figure on the left column is a full f-stop, while the indicated figures on the right at the universally accepted (for convenience) 1/3 stops.
So f1.8 is 1 and 2/3 stop faster than f3.2, hence you should use that amount a lengthier shutter speed, or 3s.

3. f/3.6 will be 2 stops faster than f/1.8, so f/3.2 will be slightly less than 2s?

4. No, two stops away from 1s is 4s (1s, 2s, 4s, 8s, etc.) So it's slightly less than 4s.

5. Thanks guys for enlightening me!

So, roughly every "1.414" times is one stop loss in light requiring doubling of the exposure time right?

6. Yes that's right. Cause apertures are measured as a reciprocal ratio of the diameter, area wise. Hence the number is achieved by a root of two, which is 1.414 etc as you point out.

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