Understanding F/Stop Calculations
If you’re someone who wouldn’t know the difference between an f/stop and a bus stop, worry not, because it is a concept that stumps many starting shutterbugs. The reality of photography is that it includes a fair amount of mathematics, an aspect that can be both interesting and confusing. Let us help clarify the concept so you can better enjoy playing with your DSLR by getting out of auto mode.
The f/stop is known by several other names including the relative aperture, the f/number and the focal ratio (f/ratio). Essentially, the number is calculated by dividing the focal length of the lens by the aperture diameter. Adjusting by one full stop will either allow in half or double the amount of light.
The standard scale of full f/stop range is as follows:
1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22
The f/1.4 setting lets in the most amount of light and f/22 lets in the least amount of light.
The focal length of a lens is defined in millimeters. For example, if you’re using a 50mm lens, f/2 is designating that the diameter of the aperture is 25mm, (50 divided by 25 equals 2.)
Understanding the basic numeric structure of f-stops will further strengthen your ability to make adjustments based upon available light. Take your camera outside and start playing with this concept and you’ll quickly see the relationship between the numbers and the results you record.