Quote:
Originally Posted by rickp1
...f stop or just stop. I'm looking for the actual adjustment setting meaning.
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Two different terms. Two different meanings.
A stop is a doubling of the light in the exposure. You can add/delete a stop of light by doubling/halving the iso or shutter speed, or moving one number of the f-stop for the aperture.
The aperture is how large the opening in the lens that lets in the light is. f-stops is a way of switching the aperture setting by stops, so you can equate it to the other settings, and uses f-numbers to describe the setting.
The f-number itself a ratio of the lens's focal length to the diameter of the aperture opening: focal_length/diameter.
So, for example, if a 50mm lens is set to f/2, that means the diameter of the aperture opening is 25mm across. If a 100mm lens is set to f/2, that means the diameter of the aperture opening is 50mm across.
The f-number means the same amount of light from the aperture across lenses, irregardless of focal length, which is why it's more convenient to describe the diameter as an f-number ratio than the actual diameter measurement; you don't have to do math to account for focal lengths. And if you solve the ratio above for diameter, it's focal_length/f-number, which is why apertures are written as
f/f-number:
f stands for
focal length. And this is also why smaller f-numbers mean
larger openings. Just as 1/8 is smaller than 1/4, f/8 is smaller than f/4.