What is ISO?
ISO is one of the three pillars of exposure, along with aperture and shutter speed.
But, unlike aperture and shutter speed, ISO doesn’t increase your exposure by increasing the amount of light that reaches your sensor.
Instead, ISO amplifies the light information gathered by the sensor, resulting in a brighter image.
Let’s examine the images below.
In the image on the right, I increased my ISO by two stops, while keeping my shutter speed and aperture constant.
By doing so, my image is substantially brighter.
What does ISO mean?
ISO stands for the International Organization of Standardization.
The name comes from a governing body that creates international standards for a variety of industries.
One of those standards includes camera sensor sensitivity.
Before ISO, there were two different standards for film sensitivity: ASA and DIN.
ISO is a combination of these two standards.
ISO and Sensor Sensitivity
There’s a common misconception that ISO controls exposure by amplifying the camera sensor’s sensitivity to light.
But that’s inaccurate. Your digital camera sensors’ sensitivity level is constant.
So why the confusion?
Before digital cameras, increasing your ISO required you to swap and change your film speed.
And ISO referred to the film’s sensitivity to light.
Since modern cameras don’t require film, ISO is no longer related to light sensitivity.
With digital cameras, increasing your ISO will not make your sensor more sensitive to light.
What it does is simply amplify the light information gathered by the sensor, resulting in a brighter image.
ISO and Exposure
No exposure setting is without its faults.
When choosing any of your exposure settings, there is always a trade-off.
For example, while wide apertures let in lots of light, they produce an image with a shallow depth of field.
When setting your ISO, the trade-off is between exposure and noise.
While increasing your ISO will make your image brighter, it will also increase the noise in your image.
There are two main types of noise.
- Luminance Noise
- Chroma Noise.
Luminance noise is directly related to image exposure and often appears as specs or static.
It is most common in underexposed images and pictures with high ISOs.
Color noise, also known as chroma noise, is uneven color transitions in an image.
It often appears as colors in areas that do not match the adjacent pixels.
This type of noise is much more dangerous than luminance noise because it can render images completely unusable.
It’s important to note that your image will experience some noise at all ISO values.
At lower ISO values, the noise is typically minor and hard to notice.
At higher ISO values, noise becomes more apparent.
This is because, at higher ISO values, you amplify both the light information and the noise in your image.
In the images above, my aperture remained the same, but I increase my shutter speed and ISO to capture an image that was sufficiently exposed image.
You can see that although increasing my ISO made image significantly brighter, it also increased the noise in my image significantly.
When looking at the image on the left the noise makes your image appear blurry and reduces the detail and texture in the image.
What is Base ISO?
The base ISO is a sensor’s natural sensitivity to light.
At the base ISO, no amplification is applied to the information recorded by your camera.
People often confuse the base level ISO with the native ISO values.
The native ISO is a range of ISO values defined by a camera manufacturer to produce acceptable images.
There is a relationship between the base ISO and the native ISO range.
The base ISO is the lowest ISO setting in the native ISO range.
I will go into more detail about the native ISO range in the next section.
The camera manufacturer does not explicitly state the base ISO for a camera, but it does indicate the native ISO range.
If you know your native ISO range, your base ISO is the lowest value on the range.
You can also do a simple google search for the base ISO, followed by your camera brand and model.
What is Native ISO?
The native ISO is the range of ISO values that uses amplification to enhance the light information gathered by your sensor.
It’s important to note that this is not one single value; native ISO is a range of ISO values.
Most camera manufacturers consider the native ISO range to produce the highest quality images.
Your native ISO will vary depending on the camera you are using.
A common native ISO range is 100 – 6400.
In some new or high-end cameras, the native ISO range may be wider.
Most manufacturer websites will clearly state a camera’s native ISO range.
So a simple google search is sufficient to find the native ISO on your camera.
I recommend trying to stay on the lower end of your native ISO range to limit the amount of noise in your images.
What is Extended ISO?
Extended ISO are ISO values beyond your native range.
Most digital cameras offer extended ISO values below your base ISO level as well as beyond your maximum native ISO value.
For example, the Nikon D800 has a native ISO of 100 – 6,400 and an extended ISO of 50 – 25,600.
This means that the extended low range is anything below 100, and the extended high range is anything above 6,400.
To achieve ISO values beyond your native ISO range, your camera uses post-processing to simulate or extrapolate what your image would look like at the extended ISO values.
In some cases, you can only shoot JPEG images with extended ISO values, but newer cameras now allow you to shoot RAW images with extended ISO.
When setting your ISO values, your extended ISO values will typically have the word “Low” or “L” and “High” or “H” next to them.
If you’re not sure what your extended ISO range is, you can look for the indicators mentioned above.
Most manufacturers and review sites will define a camera’s extended ISO.
In most cases, the extended ISO is more of a marketing and sales technique to emphasize how the newest camera models are superior to the last.
The reality is that there are very few occasions where you will need to use your extended ISO.
In most cases, your native ISO range is sufficient to reach a proper exposure.
When adjusting your aperture on most cameras, you will have the option of changing your ISO value by full or ⅓ stops.
The interval that you can adjust your ISO values will depend on the camera you are using.
Higher-end cameras may allow you to adjust your ISO by 1/2 stops and 1/3 stops.
While beginner cameras, you may only be able to adjust your ISO by full stops.
For example, the Canon T3i and Nikon D3500 only allow you to adjust your camera by full stops.
For example, the Nikon D800 and Canon EOS 6D both allow for ⅓ stop ISO adjustments.
Below is a chart with the full ISO stops and ⅓ stops.
Understanding which ISO values are full stops and which are third stops will help you when setting your exposure.
An easy way to remember the interval of each stop is only to remember the full stops.
Any ISO values outside of a full stop is a 1/3 stop.
To help you here is a list of the most common full-stop ISO values:
100, 200, 400, 800, 1600, 3200, 6400, 12,500, 25,600
Use full stops if you need a large increase in exposure.
Use 1/3 stop or 1/2 stop ISO stops for a more precise and accurate adjustment to your exposure.
In most cases, it’s unnecessary to shot with ISO’s larger than 25,600.
Even if you are shooting at night with fast shutter speeds and ISO of 6400 is typically sufficient.
How To Change Your ISO?
While the button placement for aperture and shutter speed are standard on most cameras, the same is not true for ISO.
The button to change ISO varies depending on the camera you are using.
Most cameras have an ISO button located somewhere at the top of your camera.
Another common location for the ISO button is on the navigational arrows.
Once you press the ISO button, there are typically two ways you can use to change your ISO value.
- Press the ISO button and use your aperture dial to adjust your ISO value.
- Press the ISO button and using the navigation arrows select the ISO value you want on your LCD screen
ISO buttons on top of your camera are common on Nikon and Canon’s higher-end cameras.
On the other hand, navigational arrow ISO buttons are common on Sony cameras.
What is Auto ISO?
Your camera can automatically set the other exposure settings (aperture and shutter speed) for you, so it only fits that it can also set your ISO.
No shooting mode will set your ISO for you; to achieve this, you need to use a special ISO setting called Auto ISO.
In auto ISO your camera will choose your ISO to achieve proper exposure given the other exposure settings.
Auto ISO also allows you to set minimum and maximum parameters.
These parameters act as a floor and ceiling, and won’t allow your camera to go beyond these values.
This is a great way to let your camera choose your ISO while still controlling the amount of noise in your image.
You can use auto ISO when shooting in manual, shutter priority, and aperture priority.
Depending on which shooting mode you are using, auto ISO will function slightly differently.
In aperture priority, you set your aperture and ISO while your camera sets the desired shutter speed for a properly exposed image.
When using auto ISO with aperture priority, your camera will set both your shutter speed and ISO.
When shooting in aperture priority with auto ISO use the minimum shutter speed feature on your camera.
The minimum shutter speed allows you to set the slowest shutter speed your camera will use.
This is extremely useful if you are shooting moving subjects or shooting handheld and want to prevent camera shake.
For example, if you are shooting handheld, set your minimum shutter speed to 1 over your focal length to avoid camera shake.
This will keep your shutter speed fast enough to avoid camera shake.
Using minimum shutter speed with auto ISO will give you control over depth of field and motion but you only need to worry about one settings.
This will make you much more quicker to achieve a properly exposed image.
In shutter priority, you would normally set your shutter speed and ISO while the camera sets your aperture.
This is an excellent setting if you want to control how motion is captured in your images.
When shooting with auto ISO and shutter priority, you set the shutter speed while your camera sets aperture and ISO.
For full control, when shooting with auto ISO and shutter priority, use the minimum and maximum auto ISO parameters.
In shutter priority, your camera will use your minimum ISO value and set the aperture to achieve a proper exposure.
If your image is still underexposed at the widest aperture, your camera will raise your ISO to achieve a proper exposure.
If you want to maintain a deep depth of field while shooting in shutter priority, you will need to raise your minimum ISO.
For example, if at your current shutter speed and ISO minimum value, your camera is setting your aperture to f/2.8, then your camera needs additional stops to reach proper exposure.
If you wanted to achieve an aperture of f/11, you would need to increase your ISO by four stops to achieve an aperture of f/11.
In manual mode, you would normally set all three exposure settings: aperture, shutter speed, and ISO.
When auto ISO is active, you only have to worry about setting your aperture and shutter speed, and your camera will set your ISO.
Shooting in manual mode with auto ISO allows you to control how motion is captured and your depth of field without the need to worry about ISO.
Using manual mode with auto ISO is a great way to maintain control over your image while also being able to shoot more quickly and efficiently and not having to worry about you ISO.
Be aware that auto iso in low light conditions can result in high ISO values and excessive noise in your images.
One way to combat this is by using the Auto ISO maximum and minimum features.
Most cameras allow you to set parameters for the maximum and minimum ISO values your cameras will use when in auto ISO.
This is a great way to limit the amount of noise in your shot when shooting in auto ISO.
Using the Auto ISO parameters is a great way you can stay in control while also increasing your speed and efficiency as you shoot.
I recommend keeping your minimum ISO value at 100 or your base level ISO and setting your maximum ISO to 3200.
ISO 3200 is an ISO value that will increase your exposure substantially while also not adding extreme amounts of noise to your image.
What ISO should you use?
Now that you know everything you need to know about ISO, you are probably wondering which ISO you should use.
Unfortunately, there is no one right answer.
The ISO you use will depend on the lighting conditions and image you are trying to create.
There are some instances when you should stick to using low ISO values and times where you will need to use higher ISO values.
Best Time to use Low ISO Values
If possible, you should always try to use your base level ISO.
At your base level ISO, your camera produces the highest quality images with the least amount of noise.
The base-level ISO on most digital cameras is ISO 100 or 200.
You can typically keep your ISO at the lowest possible value if you are shooting scenes with plenty of light during the day or with plenty of artificial lighting.
If there is sufficient light in your scene, your shutter speed and aperture are typically enough to capture a properly exposed image.
Even if you are shooting scenes with limited lighting, you can use lower ISO values if you are using slow shutter speeds or wide apertures.
For example, if you are shooting still images on a tripod, rather than increasing your ISO, use slower shutter speeds to achieve a proper exposure.
The Best Time to Use High ISO
If you can’t change your other exposure settings without ruining the image you are trying to capture, you will need to increase your ISO.
This often occurs if you are shooting in low light conditions or at night.
When I shoot at night as a landscape photographer, I often raise my ISO as high as 3200 to achieve proper exposure.
You may need to increase your ISO if you are shooting during low light and can’t adjust your other settings.
This is common if you are shooting wildlife or sports photography.
When shooting wildlife or sports, you typically need fast shutter speeds to freeze motion as well as narrow apertures to create a deep depth of field.
You will need to use fast shutter speed and narrow apertures you will need to increase your ISO, otherwise, your image will be underexposed.
If at all possible, I recommend you try to avoid going past ISO 6400 and ideally try to stay below ISO 3200.
Most digital cameras today can produce high-quality images with limited noise even at ISO 3200.
The rule here is that you should always try to achieve a proper exposure by first adjusting your other exposure settings.
If you can’t do so without increasing your ISO, then increase your ISO but be aware of the trade-off between noise and exposure.
Before I leave you, I would like to remind you that you
don’t need to be afraid of increasing your ISO.
An image with additional noise is better than a blurry image due to slow shutter speeds or images with insufficient depth of field due to wide apertures.