>>3874633the f-number describes the radius of the aperture opening, and there's a quadratic relationship between the radius and the area of a circle (area == pi * r^2 == pi * (focal length / f-number)^2 ).
the area is what determines how much light passes through the lens. this is why if you start from f/1, every two-stop decrease in light doubles the f-number (2, 4, 8, 16...), and if you start from f/1.4 (which is actually f/(sqrt(2)), you get doublings from 1.4 for every two-stop decrease (1.4, 2.8, 5.6, 11, 22...)
reducing the radius of the aperture opening by a factor of sqrt(2) cuts the light by ((sqrt(2)^2) == 2x, reducing the radius by a factor of 2 cuts the light by (2^2) == 4x
this is something i didn't internalize for a long time bc no one explains it that well - i actually figured it out while i was reading The Negative earlier this month. hope i didn't belabor the point too hard, i just think it's neat
pic unrelated, something from one of my first rolls in like 2018, Fuji C200 (i made a zine out of pics from this trip that precisely no one has seen)
