QUICK ANSWER
An f stop is a measure of a geometric incremented pattern based upon the powers of the square root of 2 (1.4).
This gives a geometric scale of:Â
f1.0 Â f1.4 Â f2.0 Â f2.8 Â f4 Â f5.6 Â f8 Â f11 Â f16 Â f22 Â f32 Â f45
Every stop lets in half as much light as the number goes up. E.g. f1.4 will let in half as much light as f1. A camera lens that opens to f4 will need four times the amount of light as a camera lens that opens to f2 andÂ
