Another way to term F-Stop is used is to indicate an arbitrary unit of light. If you have one aperture that allows twice the amount of line in as another, the difference between the two is said to be as 1 F-stop. In traditional aperture scale where every stop allows half as much light as the previous is as follows: 1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11, 16, 22, and 32.
Most lenses however are built to allow half-stop as well as third stop increments in between these positions. The term F-Stop is also used to measure the difference between ISO ratings where every ISO stop is twice as more sensitive to light as the last. Many new cameras allow it for one-half and one-third stop increment adjustment of the ISO.
Finally, a shutter speed which allows twice as much light as another is said to be one F-stop grader.
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