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At the beginning of this chapter, we explored a technical definition of ISO and saw what happens inside your camera when you increase your ISO setting. Let's look now at some practical ISO concerns. When you meter, your camera measures the light in your scene and then calculate the shutter speed and aperture combination that should yield an image with good overall brightness. But then shows you these parameters in its viewfinder, once it's got them all locked in. At that point, you must take note of shutter speed and assess whether it's fast enough to handle motion, the way that you want, as well as being fast enough to prevent camera shake.
If shutter speed is too low then your best option is to raise the ISO on your camera. Now, doubling the ISO setting will result in your shutter speed being cut in half, that is, if you increase ISO by one stop, then your shutter speed will decrease by one stop. It should be fairly intuitive. If the sensor is twice as sensitive to light, it can gather twice as much in the same amount of time. This means you only need half the shutter speed to gather the same amount of light that you were collecting before you changed ISO.
So raising ISO lets you speed up your shutter speed, and that gives you more motion-stopping power. To make it to the rest of this course, it's imperative that you understand where the ISO control is on your camera. Older cameras let you adjust ISO in whole-stop increments. So they might start a low ISO of, say, 100 and let you go up in full stops, 100 to 200 to 400 to 800, and so on. Newer cameras typically default altering ISO in one-third or one-half stop increments.
So you might get ISOs that go from 100 to 125 to 160 to 200. In this course, you will see that my ISO settings move in whole stops because I changed my camera's default behavior from one-third stops to whole stops. For low-light shooting, I don't typically find that the finer degree of ISO control really makes that much difference, and I like being able to think in terms of whole stops when I am altering ISO. Check your camera's manual to see if you can change your ISO increment. Now unfortunately, you can't just go changing your ISO willy-nilly, because of the issue of noise, which we discussed at the beginning of this chapter.
Therefore, to more intelligently use your particular camera's ISO, you need to better understand its specific ISO capabilities, and will be looking at how to do that in the next lesson.
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