How to understand the aperture f on the camera? I know that aperture is the amount of light entering.

F is the relative aperture, and F=f/D(f: lens focal length, d: lens diameter). The amount of light entering the lens is not completely determined by the lens diameter d, but also related to the lens focal length f. For example, a lens with a large lens diameter, if its focal length is long, the distance of light reaching the photosensitive chip is also large, so its light input is not necessarily large. or vice versa, Dallas to the auditorium So we use the relative aperture parameter f to unify all lenses. In other words, the f number determines the actual amount of light entering the lens.

Camera exposure parameters include aperture and speed, the difference between the two speeds is 2 times, and so is the two apertures, but the difference between the values is 2. This is because the area ratio is equal to the square of the diameter ratio. If the area difference between the two levels of holes is 2 times, then their diameter ratio is the root number difference of 2. This is easy to work out by yourself.