I couldn't find a source giving the definition of how much more light yields a

f1.8 vs 2.0.

I remember that each f stop represents a doubling/bisecting of light quantity.

I am confused because I just read somewhere the difference between 1.8 and 2.0 " is not so great" . So how much is it it quantitative terms??

Is a 1.8 lens only an eye catcher or is there substance to it?

F1.4 gives twice as much light as F2.0, a.k.a a one stop improvement. F1.8 is a third of a stop improvement.

As least this is what I have been told!

Thanks, the chart is enlightening!