Many of you who read this might just have bought your first DSLR and feel a bit overwhelmed at the moment. So many settings, so many factors to consider, should you just continue shooting in automatic mode and give up learning? No. I know it seems hard in the beginning, but trust me it will all soon feel natural!

This is the first part in the fundamental series.

It is actually quite simple, so let’s start today by learning ISO, perhaps the most important setting that will break your images if used incorrectly.

What is ISO?

ISO expresses your camera’s sensitivity to light. More accurate it measures the sensitivity of the image sensor. The higher the ISO number, the more sensitive it is to light, while a lower ISO makes the camera less sensitive to light.

Basically what this means is that the higher ISO you use, the quicker shutter speed you can use. With a low ISO, you need more time to get the same amount of light to hit the sensor, meaning your shutter speed needs to be longer.

You can think of the ISO as a waterwheel. When ISO is low, the waterwheel will slowly spin without dropping any water. With this method, you will transfer all the water without any loss, but it takes more time. With a higher ISO, the waterwheel will spin much faster but spilling a lot of water in the process. It works a lot faster, but with big losses of water, or a loss in quality if you prefer.

High ISO vs Low ISO

As with everything here in life, there is Pro’s and Con’s of ISO too. Ideally, I would want to keep my ISO as low as possible, preferably at 100. For most of the time, this works fine, as I always use a tripod so I can play around with the shutter speed. Other times you need to increase the ISO, perhaps you need to freeze motion or you are shooting in pitch black and want sharp stars.

Using a higher ISO leads to a higher amount of grain/noise in your image. Some people deliberately pursue this effect, while others do anything to avoid it.

Like I said in the example above, the higher you set the ISO, the sloppier your camera becomes, even though it will work much quicker. The loss in quality is significant and is more visible the higher you set the ISO.

When to Use High ISO

As I just explained, the higher the ISO, the shorter shutter speed you need.

High ISO can be used in many different scenarios, but you need to evaluate whether or whether not you can accept the added noise.

Normally I will use a high ISO when I

Photograph inside in low light

Photograph sport events

Photograph birds or other animals that require a quick shutter

Photograph during the night

Photograph during the night

These scenarios are quite different as you can see. But all of them require a higher ISO to capture a good shot – and they are worth the extra noise.

When to Use Low ISO

Whenever you do not use a high ISO.

Do I need to say more? Okey, okey!

I normally aim for using a low ISO as possible; in fact, you could call me an ISO100 nazi. It actually hurts every time I need to bump the ISO up, even though I know the results will be incredible! Low ISO means less noise, which is crucial when you are making big prints of landscapes, and it will save you hours in post production.

However, it is not always possible to keep your ISO low, especially if you are a beginner and lack essential equipment for landscape photography. If it’s getting darker outside and you don’t have a tripod, you will need to increase the ISO. If you do own a tripod though, the low ISO allows you to use a longer shutter speed which again gives amazing images.

Summary

Hopefully, I managed to explain this simple enough without scaring you away. ISO could be a very technical subject, and we could go much more into the details, but I don’t see that as a benefit, especially not if you are a beginner. If you want more technical information there are lots of articles on this subject out there.

Let’s sum things up a little:

ISO tells your camera’s sensitivity to light

High ISO gives higher amounts of grain and noise

High ISO is typically used while photographing indoors, wildlife, sport or during nighttime

Low ISO gives less noise but requires a longer shutter speed

I always recommend trying to keep your ISO as low as possible, regardless of what you are photographing. There is no reason to set it higher than needed.

Part 1: Introduction to ISO in Landscape Photography

Part 2: Introduction to Aperture in Landscape Photography

Part 3: Introduction to Shutter Speed in Landscape Photography

Part 4: The Exposure Triangle

A Comprehensive Introduction to Landscape Photography is the perfect eBook for those who are new to photography or simply want to take their photography one step further.