Have you ever had a hard time understanding ISO, and how it affects your exposure?

ISO is one of those things can sometimes seem like an abstract concept, and a little hard to understand – especially for beginning photographers. If ISO has ever been a little bit confusing for you, then you are not alone. But it is really a pretty easy concept to grasp, so let’s dive in.


First, you may be wondering: “What is ISO, exactly?” Well, basically, ISO is your camera’s sensitivity to light – so in the days of film, this was your film speed. Most of us don’t shoot with film anymore, but for those of us who are using DSLR cameras now, the same concept still applies.

exposure triangle

However, now instead of film, we are capturing images through our camera’s sensor. But even with digital cameras, we still do use ISO settings. So when we choose an ISO number, we are essentially choosing how sensitive our camera’s sensor will be to the light coming through the lens & shutter.


Here’s a quick diagram that shows inside our camera – you can see the lens, shutter, and sensor. Essentially, light travels through the lens and shutter, and reaches the back of the camera, where the sensor is – and that is what captures your image.

beginning photography tips

And this is where the ISO comes into play – allowing our sensor to be either very sensitive, or not very sensitive, to that light coming through. That’s enough explanation for now – next I want to jump straight in to some examples and show you what this concept looks like in the real world.

Now, keep in mind that there are a lot of other things we can talk about when it comes to ISO. This little demonstration is JUST going to show you the relationship between your ISO and how it affects the exposure of an image.


I’m going to start with a low ISO and then continue to increase it, so that you can see what happens to the image. With all of these images, I am ONLY changing the ISO, just to illustrate this point. I’m not changing the shutter speed or aperture, and the lighting hasn’t changed in any of these shots.

Ok, so here we are starting with an ISO of 100. And as you can see, the image is VERY dark! I almost can’t even see anything in this shot.

what is ISO in photography

So what do we need to do here with the ISO? Well, we need to help our camera’s sensor absorb or capture MORE light — or, we need it to be more sensitive to the light in this scene. Which means we’ll need a higher ISO number. So let’s continue to take our ISO higher, and see what happens.

Every time we change the ISO and take it higher, the images are incrementally becoming a little brighter each time.

ISO basics

Now as I mentioned before, there are also other things that we could discuss when it comes to ISO, such as image quality and grain – but for now we are just looking at ISO and exposure.

So as you can see, the lower the iso, the darker the image — and the higher the iso, the brighter our image becomes!

understand ISO chart

Or, to put it another way, at the lower ISOs, my camera’s sensor wasn’t as sensitive to the light, so it didn’t soak up as much light from that scene. On the other hand, as our iso increased, the camera’s sensor became more sensitive to light, allowing the camera to absorb more light from our scene, and making the image brighter.

photography basic tips

Ok you guys so that’s it for now! If ISO has ever confused you in the past, I hope this demonstration has helped you understand ISO just a little more.

Looking for more tips on ISO? Check out this post that shares more information about what your ISO means.