Pherdinand
the snow must go on
The f number refers to dividing the focal length. That's why it's called f/something.
After all, the result of focal length divided by the f/number, say, 2.8, gives a value that is equal to some theoretical lens opening (called "pupil"). That's what matters in how much light is let through to your film.
Now. The focal length, as well as the diameter of this "pupil" is a one-dimensional number. A length, a diameter.
The amount of light going through a hole, though, is depending on the surface of the hole, which relates in a square way to the diameter of it.
That's why: if you want to double the amount of light reaching your film, you have to make the diameter only 1.41 times larger - 1.41 on the square gives about 2. If you double the diameter (or halven the f-number), you get 2^2 times more surface letting light through, thus, 4 times more light on your film.
This does not work for digital, so, keep using film 😛
After all, the result of focal length divided by the f/number, say, 2.8, gives a value that is equal to some theoretical lens opening (called "pupil"). That's what matters in how much light is let through to your film.
Now. The focal length, as well as the diameter of this "pupil" is a one-dimensional number. A length, a diameter.
The amount of light going through a hole, though, is depending on the surface of the hole, which relates in a square way to the diameter of it.
That's why: if you want to double the amount of light reaching your film, you have to make the diameter only 1.41 times larger - 1.41 on the square gives about 2. If you double the diameter (or halven the f-number), you get 2^2 times more surface letting light through, thus, 4 times more light on your film.
This does not work for digital, so, keep using film 😛
