I’m going to start with a statement that you need to remember: choosing the wrong ISO will severely damage the image quality.
The aperture and shutter speed are both important for capturing pretty images but the ISO has a direct impact on the image quality. Setting the “wrong” ISO isn’t going to make the image look all that different (when viewed on a screen, that is) but it damages the file quality in a way that it’s hard to rescue when wanting to, for example, print it.
What is ISO in digital photography?
Before we talk about the best ISO for landscape photography, let’s take a quick look at what it is:
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 the 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.
Lower ISO is ideal… most of the time
Since using a high ISO is going to introduce significant amounts of noise to your image, you should always aim at using the lowest ISO possible.
You see… There isn’t one correct ISO that should be used at all times. Sure, ISO100 or ISO64 are ideal as they’re not going to introduce much noise to the image but the truth is that there are many scenarios where you need to apply a higher ISO.
This is why I repeat that the best ISO for landscape photography is the lowest possible for your given scenario.
If you’re photographing during broad daylight there’s absolutely no reason for you to use an ISO of 1600. Most likely, an ISO of 100 is still allowing you to use a quick enough shutter speed to get a razor-sharp image, even handheld.
When you’re photographing at night, though, you’ll need to increase the ISO significantly. Don’t be afraid to use an ISO of 3200 or more during those scenarios. It will introduce a lot of noise but it’s the only way to capture a sharp night sky. Just make sure that you’re still using the lowest amount that’s allowing you to use your desired shutter speed.
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How to determine the ideal ISO
So how do you figure out exactly what the lowest possible ISO for your situation is? I’ll admit this might be a bit tricky in the beginning and it’s something I often notice beginner photographers struggle with on our workshops but here’s a piece of easy advice that will help you nail the ISO in no time:
If you’re taking an image handheld you need to make sure that your shutter speed is quick enough to capture a sharp image. Typically the slowest it can be is 1/focal length. During the daytime, it’s not going to be a problem to have a quicker shutter speed than this, so keep your ISO at your camera’s native (typically 100 or 200).
When it gets darker you can keep this ISO until you need a shutter speed slower than the critical point. Once you reach this point, increase the ISO 1-2 stop and do the same with the shutter speed. At some point, it’s going to get too dark and you’ll need a tripod.
If you’re on a tripod you don’t need to worry about the shutter speed (unless you’re trying to achieve a specific look to the image). That means that you can keep the ISO at the native setting and lengthen the exposure time as it gets darker.
Learn more about the essentials of landscape photography
We’ve previously covered both the best aperture and best shutter speed for landscape photography. It’s important to have this fundamental understanding but even more important that you understand how they work together and in which scenarios you need to think differently. In our in-depth eBook A Comprehensive Introduction to Landscape Photography, you’ll learn all the essentials of capturing breathtaking images and how to apply this information when you’re in the field.