What is ISO in Photography And How to Use It

The third important setting in photography is ISO. Understanding this will allow you to produce a well-exposed photograph where it was not previously thought possible. It is the key that unlocks your potential in film and digital photography but there are some downsides to using it in difficult lighting conditions.

ISO in photography is the setting that can change the brightness of the image without physically changing the amount of light entering the camera. It defines the degree of digital amplification of available light hitting the sensor. It is useful in low light conditions but can cause noise in images.

It is important to understand your camera ISO value and how to use it correctly. Although it affects the final outcome of the image it is not technically an aspect of camera exposure as it doesn’t control the amount of physical light entering the camera. It also does not change the sensitivity of the sensor. Read on to learn more about this very useful digital enhancement tool and the pros and cons of exploiting it in your photography, particularly in darker environments.

What You Will Discover About ISO in Photography in This Article

ISO in Photography Explained

ISO stands for International Organization for Standardization which is a little confusing as the acronym does not follow the order of the words used. There were once many different standards for film sensitivity and in a move to regulate this, two of the main organization’s standards (DIN and ASA) were combined to create ISO for photography in 1974.

This was originally designed to define the sensitivity of chemical film used in film cameras but was later adopted by digital camera manufacturers to define a similar result produced by camera sensors. This would allow photographers transitioning from film to digital cameras to use ISO in a familiar and understandable way with predictable results.

To produce the correct exposure of an image there are two physical settings that we can adjust to change the amount of light that enters the camera at the moment that we depress the shutter release button. They are Aperture and Shutter Speed.

When we have exhausted the limits of these two settings; maximum aperture (minimum depth of field) and slowest possible shutter speed suitable for the type of image we desire and the exposure is still too dark, we can then bring into play the third setting that can help produce a useable image if there is not plenty of light; that is the ISO setting.

This completes the third part of the Exposure Triangle, along with Aperture and Shutter Speed.

The ISO settings on your digital camera can transform a too-dark image into a bright, apparently well-exposed image by amplifying the available light that is hitting the camera’s sensor. Raising the ISO can allow for:

  • A high shutter speed to minimise camera shake and prevent a blurry photo.
  • A smaller aperture to maximise the depth of field.

The camera’s base ISO number, usually the lowest ISO of 100 or even 50, will perform little or no amplification. The numbers then increase by doubling the ISO rating:

  • ISO 200 (Less Noise)
  • ISO 400
  • ISO 800
  • ISO 1600
  • ISO 3200
  • ISO 6400 (More Noise) (This may be the maximum ISO of your camera but some can achieve ISOs in the hundreds of thousands.)
What is ISO in Photography? Dark room interior with shuttered window and stairwell shot at ISO 1600.
ISO 1600 – 60 Seconds Exposure – Photo by Oscar J Harper

This series of photographs were taken with not much light in virtual darkness in the middle of the night. There was a very pale glow of light coming through the window shutters and down the stairwell. The light was barely perceptible to the human eye. I tried ISO 1600 as it was so dark and the lower ISO numbers would have required such long exposures that it wouldn’t have been a practical demonstration.

So, the photo above was taken at ISO 1600 for 60 seconds of exposure and the camera was mounted on a tripod. The noise levels (grain) are visible but not excessive in the shadows and the blue area. Even though it is a little dark it demonstrates how you can pull some light out of a near pitch-dark room with a higher ISO.

What is ISO in Photography? Closeup of a dark room interior  stairwell shot at ISO 1600.
ISO 1600 – Zoomed in to See The Grain (Noise) – Photo by Oscar J Harper

Above is a close-up of the stairwell light to pick out the amount of grain that has the effect of making the image slightly less sharp.

Each move up or down doubles or halves the amplification or brightness of the image. This represents a light unit of 1 stop. This, therefore, makes ISO very compatible and interchangeable with the other two settings, Aperture and Shutter speed as they can also move up and down in 1 stop increments. The three settings together give you an exposure triangle which can work together to produce the ideal image.

When the ISO is set to the higher numbers it signals to the camera sensor that the pixels should group together to improve the chances of capturing more light. This amplifies the weak light signals to artificially enhance the brightness.

What is ISO in Photography? Dark room interior with shuttered window and stairwell shot at ISO 6400.
ISO 6400 – 60 Seconds Exposure – Photo by Oscar J Harper

The above photo was taken from the same place right after the first one. Again, it was a 60 second exposure and the camera was mounted on a tripod. This time we pushed the ISO up to 6400 to demonstrate the degrading quality of the extreme noise that becomes visible at these very high ISO settings.

What is ISO in Photography? Closeup of dark room interior stairwell shot at ISO 6400 with heavy grain (noise).
ISO 6400 – Zoomed in to See The Very Coarse Grain (Noise) – Photo by Oscar J Harper

The light parts of the photograph are definitely brighter but at the expense of clarity and sharpness. The closeup above demonstrates the incredible amount of grain in the shadows and the blue lighter parts produced by the ISO 6400 and the long exposure. This would be thought to be an unacceptable amount of noise unless, of course, the graininess was a desired visual and creative effect.

The higher the ISO number the larger the clusters of grouped pixels and the greater the amplification of the light signals hitting the sensor. The grouping effect can create a grainy looking image as the clusters effectively reduce the apparent resolution and increase the aberrant pixels around the clusters. This is known as noise and it can visually degrade the appearance of your images at higher ISO numbers. Think of it as an amplifier for an electric guitar; the more you increase the volume the more distortion is produced. Shooting at a lower ISO means you will have less noise in your image as there is less digital amplification.

There are generally two types of digital sensors in electronic cameras:

  • CCD sensor (Charge Coupled Devise) – This captures photons in every pixel (known as a photosite) as an electrical charge. They are then gathered up by an amplifier at the edge of the sensor.
  • CMOS sensor (Complementary Metal Oxide Semiconductor) – Each pixel (or photosite) has its own electronic circuitry and the data recorded in each individual photosite can be manipulated individually.

How do You Change ISO on a Camera?

On a DSLR and mirrorless camera, you should be able to set the ISO yourself. It may also be possible on a good compact camera. You will need to choose a programme on the main dial that will allow you to do it. The preset programmes like Landscape and Portrait will not allow you to set the ISO as it takes care of the exposure in a very controlled manner. You should select a programme such as:

  • M (Manual Mode)
  • Av (Aperture Priority)
  • Tv (Shutter Priority)
  • P (Program)
What is ISO in Photography? Top program dial of a DSLR.
Photo by Oscar J Harper

You may have to select the ISO speed via one of the on-screen menus that are associated with the particular programme you selected. Some cameras allow you access to the settings by a quick menu (Q button). Use this method and navigate to the ISO setting section. Here you can select the desired ISO number and confirm it with the Set or OK button. You can usually choose the AUTO ISO setting here if you want the camera to select the best ISO for the current camera settings and available light.

What is ISO in Photography? Rear control panel of a DSLR highlighting the dedicated ISO button.
Dedicated ISO Button on a Digital Camera – Photo by Oscar J Harper

Some better-equipped cameras have a dedicated ISO button which you can quickly press and then use the wheel to change the ISO very conveniently. It is good practice to be familiar with how to change the ISO as it is a setting that you will probably be using a great deal to enable a fast shutter speed especially if you work in dark lighting conditions or without a tripod.

What ISO Should You Use?

It may be possible to use the Base ISO for your camera of ISO 100 or 200 which would give you the highest definition, low-noise images.

What is ISO in Photography? Night shot of the BBC offices, London, showing low grain at ISO 100.
Night Image Taken on a Tripod – Low ISO 100 – Low Grain (Noise) – Photo by Oscar J Harper

This photo was taken at the BBC building in central London at 7pm in February. It was taken on a tripod so we can afford to use a low ISO number of 100 to minimise the noise. It did require a long exposure of 25 seconds to deliver enough light but as you can see from the closeup panel, the noise is minimal.

It may just be too dark or the scene may be too fast-moving to achieve a good exposure. This is where you can “push” the ISO (higher ISO value) which will deliver a brighter image or allow a faster shutter speed without underexposing the photo. When you choose a higher ISO number the amplification of the available light is increased. You can test out different ISO settings until you can achieve an image with the perfect exposure with the desired Aperture and Shutter speed. You should avoid “pushing” the ISO too far as the resulting image may have a lot of undesirable graininess in the form of digital noise.

What is ISO in Photography? Night shot of the BBC offices, London, showing high grain at ISO 6400.
The same Image Taken on A tripod – Very High ISO 6400 – High Grain (Noise)
Photo by Oscar J Harper

As an experiment, we will shoot the same image with a very high ISO of 6400. The exposure looks the same but because of the high ISO amplification, we only require a moderately slow shutter speed of 1/3 of a second. You will still require a tripod but the speed is much more convenient to prevent motion blur of anything moving in the scene. The noise is noticeably more apparent as you can see from the closeup panel.

Just push the ISO far enough to be able to use the desired Aperture and Shutter speed. Understanding ISO will help you create a useable image in very difficult lighting conditions.

How do You Minimize Noise in Photography

We have learned that low ISO numbers produce the least noise and sharper images. Therefore if there is an abundance of available light then go ahead and use the Base ISO of 100. That is one way to minimize noise in photography.

Before you consider pushing the ISO up to a higher number you could try exhausting all the other options first. Providing that you can still achieve the desired final image:

  • Try opening up the aperture
  • Use a slower shutter speed
  • Mount the camera on a tripod
  • Use a flash
  • Photograph a more luminous scene

These actions will all allow the use of a lower ISO number and help to minimize the noise in your photographs. Try taking several test shots with different ISO numbers and check the quality of the images.

What is ISO in Photography? Night shot of a building with illuminated windows, London, showing low grain at ISO 100 using flash.
Dark Night Image Taken With a Flash – Low ISO 100 – Low Grain (Noise)
Photo by Oscar J Harper

In this experiment, we take a night photo with and without a flash. The image above was taken with a flash at ISO 100. The grain is minimal as you can see from the closeup panel.

What is ISO in Photography? Night shot of a building with illuminated windows, London, showing high grain at ISO 6400 using no flash.
Same Image Taken With No Flash – Very High ISO 6400 – High Grain (Noise)
Photo by Oscar J Harper

The grain in this photo is more noticeable as it was taken without a flash and with a high ISO of 6400. So, if appropriate, for a low noise night image, you can use a flash.

To a certain degree, there is noise in every photo at every ISO setting. You can think of it as a backdrop of interference that we need to overpower. We need the actual data of the scene (the true image without the noise) to overwhelm the backdrop of noise. The best way to achieve this is to capture more light from the scene using the exposure tools, Aperture and Shutter Speed.

It is usually better to raise the ISO when taking a photo rather than just take a darker photo at a lower ISO and then hope to post-process the image in Photoshop or Lightroom.

If you find that the available light conditions are diminishing you might consider switching to the RAW file type to store your images in your camera. This is because JPEG files already have some compression applied which causes some noise and JPEG artefacts which are made far worse with high ISO numbers. Post-production on a RAW file is much easier than on a JPEG because all of the data has been captured without any compression.

Related Questions

What is Aperture in Photography and How to Use It

Aperture is a hole in a camera that lets light in to expose the sensor or film to create an image or photograph. Its size can vary and these are called f-stops. To learn more about the creative possibilities of Aperture go here!

What is Shutter Speed in Photography and How to Use it?

The measure of the time taken to open a camera’s shutter and allow light in is known as the shutter speed. That brief moment of light provides the exposure on the sensor or film to create an image. It may only be open for a split second or multiple seconds in low light. You can control it manually or your camera can set it automatically.

It is essential to understand shutter speed to get the best out of your photography. It’s one of the three elements of photography that control the outcome of every photograph. It is fully explained here!

How do You Guarantee Grainy Photos?

Understanding ISO is a key factor in producing deliberately grainy photos. This seems to go against the general aspirations of photography but it can add some moody quality to the right subject. To find out more about this unusual approach click here to read our article in Photography Skool.

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