Knowing the f-stop scale is important if you want to quickly and accurately expose your images, however many of us have a difficult time memorizing it. If you're like me and can't remember your own phone number half the time let alone a long sequence of f-stops, then this super simple equation will help you be able to do it with ease. Filmmaker Griffin Hammond shows you how to do it in the video below:
This method of memorizing the f-stop scale is so simple that I'm wondering why I never learned it in college. As Hammond explains, all you really have to remember are two numbers: 1 and 1.4. After that, you know the entire f-stop scale, because all you have to do is double the f-number to get the next in the sequence.
1, 1.4 (That's the beginning of the sequence. Now, double them to get the next in the sequence.)
1, 1.4, 2, 2.8 (Now that you have those, keep going. You'll have to round a few numbers up/down occasionally.)
1, 1.4, 2, 2.8, 4, 5.6, 8, 11 (Yes, doubling 5.6 gets you 11.2, but we round down to 11.)
So, there you have it. Now you know how to memorize the f-stop scale using some simple math.
Source: Griffin Hammond