The amount of light that enters the camera through the aperture diaphragm is measured by f-stops. The most common f-stop values are f/1.4 f/2.0 f/2.8 f/4 f/5.6 f/8 f/11 f/16 f/22
The higher the f-stop value, the less light goes in the lens (because the aperture is smaller). The mathematical definition of an f-stop is the ratio between the diameter of the lens and the focal length.
What are f-stops and how is their value determined?
The ‘f’ stands for the diameter of the lens and the number following it is the value by which to divide it. An example: with a 50-millimeter lens, f/2 means an aperture opening of 25 millimeters (50 divided by 2). Similarly, using the same lens set at f/4 will mean that the aperture will be 12.5 millimeters. Since f-stop values are fractures, the larger the f-stop the smaller the aperture. Setting the aperture at f/2.8 will let less light than setting it at f/2. It’s time for some geometry: if you take a square and divide each of its sides by two you’ll end up with four smaller squares. This is consistent in other shapes as well and also with the aperture in your camera – if you half the diameter of the aperture the reduction in the light will be more than by a factor of two. So setting the aperture at f/2 lets in four times more light than setting it at f/4.
To summarize, there are two key things to know about f-stops:
- The higher the value the smaller the aperture and the less light that gets in.
- Every single-step reduction in the f-stop value reduces the amount of light by a factor of two.
An f-stop table for different lenses
The following table details the aperture diameter for certain lenses set at certain f-stops:
The f-stops influence the sharpness of a photo
The f-stop you choose will directly influence the sharpness of the resulting photo. A higher value will let less light in and objects in the photo will look sharper, a lower value, on the other hand, will let more light in causing the object that’s in focus to be very sharp and the rest of the photo to be out-of-focus. This is a wonderful way to shoot outdoor portraits, such as your kid in a field of tulips. Your kid’s face will come out sharp and the field of tulips will be out-of-focus. You can further your knowledge on this topic by reading about aperture. Now that you know more about f-stops, expand your knowledge of photography and read up on photography lessons, including composing shots and leading lines. Even simpler – click here to sign up for a free email course and get weekly photography lessons straight to your inbox including tips and exercises.