The ISO setting on your camera helps you expose your photographs correctly. ISO can also effect the look of your photography and plays and important part in night-time photography.

Understanding camera ISO will help you understand how to better expose your shots.

What is ISO?

Camera ISO measures the sensitivity of a camera’s image sensor. The ISO setting will brighten or darken a photo. As you increase ISO, your photos will become brighter. In low light settings using a higher ISO can help you keep your shutter speed high while avoiding taking underexposed photos.

Be aware that as you raise ISO, grain (or digital noise) will appear in the photo. So, raising ISO becomes a trade-off. You should try to adjust aperture or shutter speed before increasing ISO too high.

What does ISO stand for?

ISO stands for International Organization of Standardization. They are the main governing body that standardises the sensitivity ratings for camera settings. The term originated from film when the ISO rating was called ‘film speed’.

Having a standard for sensitivity means you can shoot the same ISO on different cameras and know the exposure will be equal.

What is Base ISO?

The lowest ISO you can select on your camera is known as the base ISO. Using the base ISO will give you the highest image quality for your camera and also reduce digital noise. When shooting, start with your camera on this base ISO and only increase it if the conditions require it.

The standard base ISO on most digital cameras is 100, 200. Some cameras offer a base ISO of 50, but there isn’t much difference between 50 and 100.

How ISO effects exposure

ISO makes up part of the exposure triangle and is one of three factors in determining the exposure of a photograph. Camera ISO affects the sensor of the digital camera, while aperture affects the lens and shutter speed affects the exposure time.

ISO works similarly to shutter speed, as when ISO has doubled the exposure (more or less) is also doubled. A high ISO setting will equal a high exposure and a brighter picture, whereas a low ISO will result in low exposure and a darker picture.

The examples below show how increasing ISO will affect your photos. Not only does the brightness increase, so does the amount of digital noise.

example of a photo at ISO 100
ISO 100
example of a photo at ISO 4,000
Example of ISO 4,000
example of a photo at ISO 20,000
ISO 20,000
example of a photo at ISO 40,000
ISO 40,000

So I can’t ever use a high ISO?

There will still be occasions you will need to use a higher ISO to get a decent exposure. Cameras with larger sensors handle the noise better. Improvements in technology are making digital noise less of a problem than before. It is a good idea to test your camera in low light conditions to find out the highest ISO setting you feel happy with.

Also, remember that sometimes grain can be an artistic element, but I would recommend trying to keep your ISO in a range between 100 – 400. Lower ISO equals lower sensitivity which equals higher quality photos.

What ISO should I use in low light?

You will want to shoot at the lowest ISO possible at all times. But some conditions will force you to make concessions, low light for example. Because there is less light, you will have to photograph with a higher ISO to compensate. Be careful because the more you increase the ISO, the more digital noise will appear.

That doesn’t mean that you can’t take crisp, high-quality pictures in low light, it’s often quite the opposite. The hour before the sunsets, known as the golden hour, is a favourite time to take photos.

When shooting in low light, you can adjust the other two sides of the exposure triangle to help you keep a reasonably low ISO. By using slower shutter speed and using a smaller f-stop, you can let more light into your camera sensor and allow you to use a lower ISO. Of course, these changes will also change the feel of the photo, so be willing to test your settings to make sure you get the best shot possible.

What is Digital Noise?

fountains in washington dc shot at night

In digital photographs, “digital noise” is the term used to describe visual distortion. It looks similar to grain found in film photographs. It can also look like splotches of discolouration when it’s at its worst, both of which can ruin a photograph. Noise tends to get worse when you’re shooting in low light.

Which ISO should I use?

Sorry, but there is no one answer to this question. While I will recommend keeping your ISO in a range between 100 – 400 there are times this is not possible. Bear in mind these factors when selecting your ISO.

  • Lighting – What are the light conditions? Is it low light or is the subject well lit?
  • Noise – Is this a photo you want without noise or would grain be acceptable
  • Tripod – Are you using a tripod?
  • Motion – Is the subject moving or standing still?

Try and remember the factors that will determine your ISO selection because, as with most photography, different situations will require different settings. The fun comes in experimenting with each setting and creating a style you enjoy.

When to shoot low ISO

You should always try to use the lowest base ISO on your camera; this will be typically 100 or 200.

If you have a strong light source, you can choose any ISO you want.

In dark and low light conditions it’s still possible to shoot with a low ISO. Stabilising your camera lets, you use a slow shutter speed, which lets more light into the camera. More light means you can lower your ISO and increase picture quality by reducing digital noise.

When to shoot high ISO

In the ideal conditions, you will always use a low ISO, but there are occasions when you need to use a high ISO. One reason is to beat motion blur. When photographing an action scene, your choice will be a sharp photo with higher iso or a blurry photo at low ISO. The faster shutter speed you use, the less light you let into the sensor. To balance that lack of light, you will need to raise your ISO.

If you want to shoot a sports event, you will need to use a high shutter speed like 1/1000 or above. If you’re going to carry on using a low ISO like 100 or 200 you’d have to use a slow shutter speed like 1/100 and then your pictures would blur.

Shooting at night in low light is another occasion when you will need to increase ISO. Stabilise your camera to shoot with a slower shutter speed, but in the darkest conditions, this still won’t be enough light, so you need to increase your ISO. Be careful here because in low light increasing your ISO will quickly add digital noise to your photo.

Modern digital cameras will have an auto ISO setting. The camera will automatically decide the best ISO setting depending on your aperture and shutter speed. It’s possible to set a maximum ISO that the camera will never go over. To compensate for this, your camera will slow your shutter speed, and that can introduce blur or camera shake. That’s the exposure triangle; it’s all a balancing act.

What ISO is too high?

This will depend on the lighting conditions. During the day or in bright light, an ISO of 1000 will be too high. At night or in low light situations you might need to use an ISO of 3200. It also depends on how much digital noise you are willing to accept in your photo. Most people will say they will take a sharp, noisy picture over a clean, blurry one.

As with a lot of aspects of photography, it will come down to personal choice and testing. I will start with my ISO on 100 every time I start shooting. Then depending on the conditions, I will adjust my ISO accordingly.

You can adjust aperture or shutter speed to help you keep a low ISO, but using a slow shutter speed can lead to blurry photos if you don’t have a way to keep your camera steady. You can also use a lens filter to adjust how much light hits your camera sensor, giving you more options for your ISO setting.

new york city skyline shot at dusk from brooklyn
boston city skyline shot at night

Both of these photos are taken with an ISO setting of 6,400. While there is digital noise visible in the first photo, it is much more noticeable in the second photo.

These two photos show that even using by using the same ISO you can get a different amount of digital noise. Different conditions will mean you will have to test and adjust your ISO setting.

ISO and shutter speed

ISO and shutter speed are two parts of the exposure triangle. As such the two settings work together to achieve your ideal exposure. Using a slow shutter speed is an effective way to maintain a low ISO. By slowing the shutter speed, you will let more light into the camera sensor. That means you can keep your ISO low and reduce the digital noise in your picture.

When shooting in low light conditions or at night even using a slow shutter speed may mean you will have to use a higher ISO than you are used to. In this instance make sure you properly review your photos.

There is nothing more frustrating than coming home from a shoot and realising your photos don’t look the way you wanted. Review your photos on-site and if you’re not happy continue to test your settings.

ISO and aperture

Aperture is the third part of the exposure triangle. As you reduce or increase aperture you can also change your ISO. By increasing aperture, by selecting a lower f-stop number (yes increasing aperture means lowering your f-stop – it can be confusing so check out my aperture guide) you will let more light into your camera sensor. This will allow you to keep a low ISO setting.

As you increase aperture, you will reduce the depth of field in your photograph. This will change the look and feel of your photo. You will need to be aware of the different effects changing your aperture can have on your photo.

Sometimes you will have to accept some digital noise to get the look and feel of the photo you want.

Understanding camera ISO key points

  • Start shooting with a low ISO setting (between 100 – 400) and then make changes if you need.
  • When you are finished shooting set your ISO back to 100. It can be incredibly frustrating to start shooting during the day with your ISO set too high from a previous session.
  • ISO makes up part of the exposure triangle. As you adjust one setting, you will have to compensate with another. Learn how ISO works with aperture and shutter speed.
  • Sadly, there is no easy guide to what ISO is best. Conditions vary considerably meaning you will have to shoot and test with different settings to get your best shot. The more you practice this, the quicker you will be able to judge what settings you need.
  • The lower your ISO setting, the less light is let into your camera sensor, and the less digital noise will appear. The higher your ISO, the brighter the exposure and the higher the amount of digital noise.


ISO makes up part of the exposure triangle but it will also effect your photos in other ways. The amount of ISO will also impact look of your photos. By understanding camera ISO you can start to have more control on the look and feel of your photographs.

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