Quote:
Originally Posted by hallsworthb
Just to satisfy a yearning in me for a last dot on the "i" and cross on the "t" - Please define a "stop" - I thought that was relating to "F" stop - The aperture set on the lens?
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It's half or twice the amount of light and it doesn't just refer to the aperture (although when people talk about "stopping down" they do mean the lens).
Aperture-wise f/4 lets twice the amount of light through that f/5.6 does. f/5.6 lets through twice the light of f/8 etc.
Shutter speeds and ISO also work the same. 1/500th of a second is exactly twice as much light as 1/1000th of a second. ISO200 is twice ISO100. ISO400 is twice ISO200 etc.
I wrote a tutorial on this (and I'm going to link to it twice in 1 day!) which you can read
here