ISO - Taking Better Pictures Tutorial 1c

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ISO - Taking Better Pictures Tutorial 1c Empty ISO - Taking Better Pictures Tutorial 1c

Post by travis_cooper on Mon Feb 25, 2008 10:53 pm

ISO is the last element that gets you your exposure. ISO is also known as film speed, it basically determines how sensitive your film, sensor, is to light. The more sensitive it is to light the "faster" it can capture the data, so using fast film speeds means you are in a way adding light because the film is sensitive enough to get the data faster. The downside is that you lose color saturation and you start getting little grain like spots. In the digital world this grain is known as noise.

ISO values are pretty easy to remember because each full stop is just double the one below it. Each camera will probably have a different range, but most will have the values between 200 and 800. Here are the values.

50 Low ISO - less sensitive to light so we need slower shutter speeds, also means less noise
3200 High ISO - more sensitive to light so we can use faster shutter speeds, also means more noise

In the next examples I kept my aperture value the same so as I switched ISO values the shutter speed changed. Also look for the noise in the second shot.

This first shot was taken at ISO 100. This meant I had to use a slower shutter speed, but I had it on a tripod so it didn't matter.
ISO - Taking Better Pictures Tutorial 1c _IGP1164low-res

Now I bumped my ISO up to 1600. This made my shutter speed four stops faster, but also made the picture noisy.
ISO - Taking Better Pictures Tutorial 1c _IGP1165low-res

Notice how the second shot has the little grains we refer to as noise. Also notice that the darker areas are noisy than the lighter spots. For example the right part of the tape measurer is where the light was directly shining, so it doesn't have much noise at all, but as you move to the left and the light falls off we start getting more and more noise.

So for a recap, ISO allows you to get more stops of light. Usually this is used to get you faster shutter speeds. However, for these higher shutter speeds you have to pay for it by getting noise in your shots. I would actually strongly urge people to never bump up their ISO unless they absolutely have to. If there is motion that you need to freeze and you just can't get a fast enough shutter speed to stop it. If there is no motion in the shot I would much rather put the camera on a tripod and keep the ISO low than raise the ISO.

Setting your ISO isn't as common as setting shutter speed and aperture, so usually it isn't as quick to do. You will need to read your manual to see how to change the ISO. A lot of cameras will have it set to auto, where it will try to pick a value to give you a faster shutter speed. I would suggest changing it to 100, or whatever your lowest value is, and leaving it there unless you really need to change it.

Again post any of your ISO specific questions, or images, here so others can learn from the answers.

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