Tips and Tutorials

Understanding ISO – The Beginner’s Guide

ISO is one of the 3 pillars (the other two being aperture and shutter speed) of exposure and understanding how ISO affects your photography is key to capturing amazing images! In the following article I will give you a beginners guide to ISO to help kick start your photography!

  1. What is ISO?

In the most basic terms, ISO determines how sensitive the image sensor is to light. The lower the ISO number the less sensitive it is to light. The opposite occurs with higher ISO numbers, the higher the number, the more sensitive the image sensor is to light. With the higher ISO numbers, you have the ability to capture images in very low light as the sensor is able to take in more light during an exposure. High ISO photography can be very useful in a number of situations, but also has its limitations, something that we will cover shortly.

Below you can find a side by side image that shows the difference between low and high ISO.

The image on the left was taken at ISO 3200 and the image on the right is taken at ISO 100. The difference is a little hard to tell unless you look closely, so take a look a little closer and crop in:

Now the difference is clear! Can you see that speckling on the left? That’s image noise from a high ISO setting.

Each camera has a setting called the base ISO, this is typically the lowest ISO number (in many cases ISO or 100 or 200). The base ISO gives you the best Image quality, the highest dynamic range (amount of light and dark captured in one image), best color depth (number of colors reproduced) and the cleanest image with the least amount of noise. Whenever possible try to use the base ISO, this will get you the best image quality. Unfortunately, this is not always possible, especially when your hand holding you camera and not on a tripod.

In most cases cameras will have the ISO steps 100, 200, 400, 800, 1600, 3200 and so on. As we move up each ISO step the sensitivity will effectively double, allowing twice as much light in. So ISO 200 is twice as sensitive as ISO 100, ISO 400 is four times more sensitive as ISO 100 and so on. The increased sensitivity allows for significantly more light, and therefore you can capture images in darker environments.

2) When to use low ISO

I mentioned above that it is best to use the base ISO, which is typically ISO 100 or 200 (in some cases 64 or 32), whenever possible. For instance on a bright day there is no reason to increase the ISO. Keeping the ISO low will give your best sensor performance and the most detail. Other times that you can use a low ISO is when you are on a tripod. In that case you are no longer required to have a minimum shutter speed to keep your images free of motion blur and the added detail gained from the low ISO setting will be very noticeable in your final image. Take a look at the image below:

Even though this image was taken at sunset, I used the base ISO of my camera. This gave me the extra detail to make large prints of this image, but it also helped with my post processing. The added dynamic range that occurs at base ISO allowed me to increase the brightness of the shadows significantly, something that took this image from unusable to usable!

3) When to increase ISO

Now there are times when you just don’t have enough light to get usable images at your base ISO. Anytime that you do not have a flash or studio lights to add light, or have a very fast lens to allow more light in you should increase your ISO. For instance, if you’re shooting a wedding reception indoors at night, the mood lighting that gives the reception its ambience, is a nightmare for photographers. Generally a flash doesn’t help in this situation, so increasing the ISO is the next best thing. Another situation may be if you’re shooting street style images. The image below was captured in a very dark alley and I didn’t have a tripod with me, so I increased the ISO to 1600 and was able to capture the image I wanted.

Before you increase the ISO, consider if you are okay with introducing noise to the image. In the above image, I knew that I was going to convert it to black and white, and decrease the brightness to make the shadows very dark, all of which help to hide the noise.

Another situation which would warrant increasing the ISO is taking wildlife images. Consider the image below; I was using a 500mm lens, handheld on an overcast day. If I kept the ISO at its lowest setting I would have introduced motion blur from the moving foxes, or the fact that I was handholding the lens. Instead I increased the ISO to 1600, allowing for a high shutter speed to freeze the foxes in motion.

If you have any questions, comments or feedback, please post them in the comment section or send me a message and I will do my best to get back to you! Remember that this is a basic overview of ISO and is not meant to be the be all and end all. There are plenty of resources out there if you’re looking for a more in depth explanation.