ISO determines how sensitive the camera sensor is to light. Having a higher ISO setting becomes very useful when shooting in low light situations. With standard DSLR cameras, ISO settings can range between 100 and 25600. Higher end DSLR cameras can have as low as 50 and as high as 204800. The lower the ISO, the smoother the image quality. The higher the ISO, the more sensitive the camera sensor is to light. This means you can capture images in very low light situations.
- In this example, at ISO 100, the image is at its smoothest state.
- At ISO 1600, noise starts to appear in the darker tones and becomes easily noticeable.
- ISO 12800 makes the image no longer usable. The image has suffered from too much noise.
But there is a downside; lower ISO settings make the camera sensor not as sensitive to light. This results in smoother pictures but the images are prone to shakes and blurry images since the shutter must stay open longer just to get enough light to the sensor. Having a higher ISO setting lets you capture images in low light situations, but also causes the image quality to have a lot of noise. The higher the ISO, the more noise an image will have; this is not audio noise, but the tiny little dotty bits that appear on an image.
In this sample image on the right, I used the same images from before but instead I magnify a certain spot to allow you to see what I mean by “noise”. Notice how the image taken under ISO 100 has no noticeable noise while zoomed in. The image looks very clean even when it is magnified this close. New cameras with better technology can maintain a clean image even at a very high ISO.
Now look at the second image taken under ISO 12800. It is the same image but taken at a much higher ISO. Notice how there is a great amount of noise all over the magnified image. In darker situations, you would not notice as much noise, but I am just shooting at a high ISO in a well-lit area for the sake of this comparison.
Cameras with better image processors technically perform better in ISO performance than a camera with an older image processor. For example, a newer camera will have a smoother image than an older camera if they are both taken at ISO 1600. So if you plan to take pictures in well-lit areas, you do not need an expensive camera with good ISO performance. If you find yourself taking pictures in low-lit places, then you should consider a more beefy camera with better ISO performance. The best way to find out is to test a camera with a couple other cameras within a similar price range.