>>3163338>shutter, ISO, and f-stopThey're all generally measured in "stops", which represents halving or doubling of the light in an exposure. I.e.,
Going from 1/100th of a second to 1/50th of a second is one stop (shutter open for twice as long, lets in twice as much light). 1/25th is another stop. 1/12th (roughly) is another.
Similarly, going from ISO 100 to ISO 200 is a stop (makes the sensor twice as sensitive). ISO 400 is the next, then ISO 800, etc.
F/stop is a little more confusing since one stop is represented by multiplying it by the square root of 2. The easy way to remember the sequence is that sqrt(2) is about 1.4 and sqrt(2)*sqrt(2) is 2, so start with 1.0 and 1.4 and alternate doubling them:
1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8, 11, 16, 22
Going from each of those numbers to the next smaller one is one stop.
So if you're at the exposure you want, for each stop you go UP in one leg of the triangle, you have to go DOWN in another, and vice versa. So if you want to use a shutter speed that's twice as fast, you need to open up your aperture by one stop or increase your ISO by one stop, for example.
Modern cameras usually let you set your settings in third-stop increments (sometimes they limit you to full stops for ISO, but it depends on your camera and your camera's preferences). In your viewfinder there should be a meter display that's a little set of lines like a ruler. The long center line is what your meter considers "correct" exposure. One direction represents underexposure from that, the other overexposure (although always remember that the meter doesn't represent "correct" exposure so much as "your camera's guess for what's good enough". The actual "correct" exposure is whatever you think looks good based on your artistic preference for that shot).
Let me know if the answer to your question wasn't actually in that wall of text.
