ISO is a function on your camera that works with your aperture and shutter speed. All three of those controls allow you to change how much light you capture when you take a photograph.
When you change your ISO setting, you can increase or decrease the amount of light you will get in a particular photograph.
In other words, what the ISO does to your pictures is make it brighter if you increase the ISO or darker if you’re turning it down.
A lot of people say that the ISO changes how sensitive your camera sensor is to light. Now that’s not technically true, but technically it doesn’t matter because practically, what happens is when you increase your ISO, you get more light in your picture. This is super helpful because in some situations you just need more light in order to get a sharp photo. When we’re shooting in low light. We’re often fighting to get a shutter speed that’s fast enough to allow us to capture a sharp image.
If you’re able to increase the ISO, which gets you more lighting your image, you’re then able to bring up that shutter speed and often get it to that place where you can capture sharp image.
So let’s take a look at what the numbers for ISO actually mean.
Typically a camera starts with a low ISO of something like 100, (and the lower the number is, the less light you’re going to capture), and then as you go up the ISO scale, you will get more light, but how much let you get will depend upon the number you choose.
You have these whole numbers like 100, 200, 400, 800, 1600, and then you have these in between numbers like 125, 160, etc…
The whole numbers are full stop increments, meaning, if you go from 100 to 200, you’re going to get twice as much light in that photograph, and if you go from 200 down to 100, you’re going to get half as much light.
Now those in between numbers give you finesse in choosing how much light you want to add. Sometimes you may just want to go from 100 to 200 and double the brightness of the image. But sometimes you just want that image to be a tiny bit brighter. And if you want it to be just a tiny bit brighter, you can go from 100 to 125. That is a one third stop change.
Now, one of the questions I get all the time is, “How do you know what ISO to choose when you’re out taking pictures?”
This is actually pretty straightforward, but the thing that catches people up on this is getting too obsessed with the noise, and we’re going to come back to the noise in a minute, but first we’re just going to talk about choosing ISO.
Generally speaking when you’re in very bright conditions like in full sun outside or in very well with rooms when you’re indoors taking photos, In those situations, you generally want to choose a lower ISO setting.
It logically follows then that if you’re shooting in a low light situation where it’s quite dim, like at night, or in a dim room, that’s when you would want to increase your ISO.
The idea here is that you want to choose the lowest ISO possible but the highest ISO necessary for you to get the photo, and as I mentioned earlier, when we’re shooting and lower light situations, where we tend to have to increase the ISO, we’re fighting to get a shutter speed that will allow us to capture sharp image.
So what you want to do is increase the ISO to the point that you’re able to get a shutter speed that will allow you to capture sharp image.
And this brings us to the noise because most people know that when you are shooting at higher ISO, you get noise introduced into your image. Noise is digital artifacts, randomness in the signal generated by the camera sensor when you’re taking a photograph, and the higher your ISO is, the more prevalent that noises is in your image.
Most people want as little noise as possible in their images, which I totally understand, but in some cases, you just need to shoot at a higher ISO, which is why you want the lowest ISO possible but the highest one necessary.
Your camera is an amazing tool, but it’s no good to you if you don’t know how to use it!
If you want to take control of your camera and use it to take amazing photos like a pro, check out my Guide to Shooting in Manual Mode video course.