The basic relationship between f-stop (aperture) and exposure time is one of the more critical relationships in photography. F-stop is measured as a number that represents 1/n of the focal length. Doubling the size of the number halves the diameter of the f-stop, but because it’s a ratio, you count lockstep from 1 and 1.4. That is, from 1 to 1.4 is a full stop, then 2, then 2.8, then 4, then 5.6, and so on. Exposure time is measured in seconds or fractions of a second (for this, I’ve just used round multiples of some exposure time t). As you halve the size of the aperture (double the number), you need to double the exposure time in order to get the same exposure, or leave the exposure time the same to get half as exposed an image. “Full stops” are yellow, “half stops” are light blue. A future diagram will cover some of the other variables that come into play here, but this is the basic relationship. I’ve illustrated the relationship across the wide/middle part of the range.