What is f - Number?
Monday, July 7, 2008 @ 20:50
The - f - number is also referred to as the focal ratio and it is the ratio of the diameter of the lens aperture (or opening) to the length of the specific camera lens. Of course, this number will change based on the lens used at any given time, and it is something that the photographer can alter by simply changing the f-stop setting on the camera's lens. Each individual increment of an f-stop (as well as the f-number) represents an incremental decrease in the amount of light entering the lens by half of the previous intensity.
Most camera lenses have f-stops that are represented mathematically by integral powers of the square root of two. Of course, the mathematicians have fun coming up with these sorts of calculations, but for us normal types this merely means that some of the more common f-numbers you will work with are f1, f2, f4, f8 and onward. As you can see, the f-stops double as the number gets larger ... f1 increases to f2, and f2 increases to f4 and so on; the lower the number the larger the aperture.
The f number is very important because it allows the photographer to control the amount of light he allows to enter the camera lens. In conjunction with controlling the f number, the photographer also adjusts the shutter speed. The more light allowed reaching the camera lens, the faster the shutter speed should be set so that the film is not over-exposed.
As we evolve in our knowledge of both the gear we work with and our skill as photographers, we soon see the necessity of controlling such things as exposure and how the settings we select will impact not just the quality of the images we take, but also the special effects we use to make those images more stunning.
