I so confused, too. Sorry, bad humor, I know. Today I’d like to give a very basic explanation of what ISO is and how you can use it in your photography.
In digital photography, ISO refers to how sensitive the sensor is to light. The higher the ISO, the more sensitive to light. ISO is one of the three components that combine to form the exposure of a photograph, along with aperture and shutter speed. Understanding these components and how they interact can help you take better photographs.
The higher the ISO, the brighter your photos will be, all other things kept equal. This sounds like a good thing, right? It is, to a point, but only to a certain extent and only under certain conditions.
There is a disadvantage to turning up the ISO. The higher the ISO, the more noise there is in the photo. Noise is anything that appears in the photo that was not in the actual scene, usually giving the photo a grainy appearance. How high you can increase the ISO before noise becomes a problem varies based on the camera, the largest factor being the sensor size of the camera. An expensive professional camera with a large sensor may be able to go up to ISO 3200 without noticeable noise. On the flip side, a cheap point and shoot camera with a small sensor may not get past ISO 400 without noise becoming an issue.
The two photos above were both shot on a tripod in a dark room. If you look closely you can see the noise on the photo shot at ISO 6400, especially near the top of the photo. It isn’t too bad since it was shot on a fairly nice camera but if you look at the zoomed in photo below you can definitely see the increased noise on the top half which is from the ISO 6400 photo.
Does this mean that high ISO is bad? No, of course not. Look at the first image comparing the two photos again. Yes, there is noise there but if you weren’t looking for it, the noise wouldn’t be that noticeable. Let’s go back to the beginning again. A higher ISO means more light. The other ways to get more light to get the correct exposure are by adjusting the aperture or the shutter speed. The aperture on these photos was already as large as it could be so the lower ISO on the left hand image meant the shutter speed was slower to allow enough light into the camera. What if the camera hadn’t be on a tripod?
There is the result. Because of the slow shutter speed the photo came out blurry. And the blurriness is much more noticeable than the noise in the image above. This is an example of a time when it makes sense to crank up the ISO even if it means there’s a little noise. Any time you’re shooting poorly lit scenes by hand and don’t want to use flash (or the subject is far enough away that flash wouldn’t be effective), it’s better to have some noise than a blurry picture. Or if you are using a tripod but there are objects in your photo which are moving, you may be better off with some noise but those objects being sharp instead of coming out blurry.
On the flip side, there is no point in using a higher ISO in brighter scenes (a sunny day, for example) when there is already enough light coming into the camera. If you’re using a tripod and shooting a stationary subject, keeping the ISO a bit lower and allowing a longer shutter speed may provide a better result. Most cameras automatically adjust the ISO pretty well on their own, staying at ISO 100 in any fairly bright scene and only increasing it when the lighting of the photo you’re taking needs it. However, it’s a good idea to keep an eye on it, especially in darker scenes were you may want to make it higher or lower than what your camera thinks it should be.
I hope this makes ISO a little more clear, understanding how ISO works is a key tool to understanding how to get the most out of your camera. I not so confused, now.
Until next time, happy shooting.