>>3704010Very cool and thorough answer my man. Nice contribution.
>>3704008f/ numbers are a fraction. The F in F-stop actually refers to the focal length. So when you see f/1.8 on a 50mm lens, you're actually reading it as 50/1.8. The entire fraction refers to the apparent diameter of the entrance pupil as viewed from the front of the lens (which is why wide lenses get slower as you get wider).They proceed in a geometric scale, specifically the square root of 2, which is 1.414. It goes f/1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64, 90, 128. Each f/stop gets half as much light as the one before it, so f/5.6 is 16 times darker than f/1.4.
You see weird numbers like 1.8 because lenses are often measured in 1/3-stop increments. They're also often just rough approximations, and f/1.8 might actually be f/1.76 or f/1.93, depending on the lens. They are also rough approximations in terms of light transmission and overall exposure. The same f/stop on several different lenses will yield several different exposures, within a few thirds of a stop of each other. This isn't such a big deal for photography where we can jut change shutter speeds, but it's a big deal for video and film. Instead of f-stops, you'll see T-stops used in cinema, which is an F-stop, corrected for the transmission of the lens (f/1.8 might be T/2.1, for example).
F/stops also affect depth of field. The smaller the entrance pupil, the greater the depth of field. You don't really need to know why it works, just know that it does. f/16 will have almost everything in the frame in focus, while f/1.4 will have only a very narrow sliver.
Lastly, f/stops affect the sharpness of your image, though far more people worry about it than need to. Generally, lenses are sharpest around f/8 and start to soften towards either side of the scale. You likely won't notice this unless you stop all the way down to f/22 or shoot wide open.
