Here is a short diagram for showing the relationship between F-number and what's happening in the real world...
F-number = f/D
where f is the focal length, and D is the diameter of the entrance pupil (aperture)
let's take a simple example:
if
F-number = 1, f = 100mm, D = 100mm, Aperture = Pi*(D/2)^2 = 2500Pi
So in order to get an aperture with half size,
1250Pi = Pi * (D'/2)^2, and
2 * Pi * (D'/2)^2 = Pi * (D/2)^2
D' = 1/(2)^0.5 * D
This gives about D' = (1/1.4) * D
and this is so called "1-stop" decrease in light! Thanks for reading!
****
If you think that this passage is good, please help and click the sponsors on the right hand side for support. Thanks for reading!
****
Good photo comes from our soul, NEVER from our camera.
