ISO in Photography: Crafting the Perfect Exposure

(Last updated on July 5th, 2022)

Creating a well-exposed image can be a challenging task for a beginning photographer. If you have never picked up a camera, the dials and buttons may seem foreign.

In order to become a good photographer who can create perfectly exposed images you have to know about shutter speed, aperture, and ISO. These three foundational settings create the exposure triangle.

Shutter speed is self-explanatory. The aperture is the size of the lens opening and controls how much light enters the lens and the depth-of-field. The ISO is not that simple. This article offers an exploration into what the ISO is and how best to use it to create not just well-exposed images, but ones with the highest image quality a camera can make.

ISO and Photography

ISO stands for International Organization for Standardization. Historically, there were three film standards, ISO, ASA, and DIN. In 1974 they were combined. The term ISO is the same across all languages.

In order to have a properly exposed image, you must set the ISO in your camera settings before creating an image. This differs from the days of film when the ISO was fixed across an entire roll of film. This has led to misunderstandings about what the ISO actually does digitally.

With film, ISO refers to how sensitive the film is to light. A 100 ISO film is typically used in bright, well-lit scenes. Landscape photographers typically use lower ISO films to produce higher quality images. Yet low light conditions, such as a concert or night time wedding reception, called for higher ISO film, closer to 800 or 1000.

Increasing the ISO makes the film chemically more sensitive to light. Thinking about ISO this way does not translate as simply to digital cameras.

Many photographers today incorrectly say the ISO refers to the light sensitivity of the sensor. This is inaccurate.

Nikon explains it succinctly: “Digital cameras convert the light that falls on the image sensor into electrical signals for processing. ISO sensitivity is raised by amplifying the signal.”

When the ISO is doubled, say from 100 to 200, the electrical signal is doubled, or amplified. This means that half as much light will be needed to achieve optimal exposure. While a higher ISO does help the sensor create an exposure in lower light it is not more sensitive to light.

The Exposure Triangle

Before we get any further, we need to talk about the exposure triangle. Composed of three settings: shutter speed, aperture, and ISO, this triangle helps visualize how a change in ISO affects exposure.

As the ISO increases, the exposure needs less light to create a balanced histogram. To achieve this, the shutter speed and/or the aperture are changed to compensate.

Exposure Triangle
Exposure Triangle

Common ISO Settings

The ISO is a powerful tool for digital photography. Most cameras out today have a range of 100 to about 25,600. This range is known as the camera’s native ISO range.

Cameras from different manufacturers have different native ranges. The range is dictated by the design of the sensor. Some cameras go higher and lower. These numbers are commonly referred to as ISO speeds.

ISO 100Best used in bright lighting conditions, such as a sunny day or with flash.
ISO 200 – 400Good for overcast days or well-lit interiors. Could also be used with macro photography. 
ISO 800-1600Best suited for low-light situations, such as interiors and concerts. Could also be used for bird photography.
ISO 3200 – 25,600These higher ISO values are most commonly used with astrophotography and nighttime street photography.

Remember when the ISO speed is doubled, the sensor doubles the amplification. This is a one stop increase in exposure. For example, an image created at 800 ISO will be twice as bright as one created at 400 ISO, if no other settings are adjusted. Many cameras have extended ISO ranges that go above 25,600 or below 100. While this may increase or decrease the exposure, it does so at a cost to image quality.

When the ISO is extended beyond the native range the camera is simply using software to expand the electrical signal. It is identical to the process of lifting the exposure in Lightroom or Photoshop. Since it is done at the time of image creation, it locks the potential damage into the RAW file.

Base ISO

Camera manufacturers create what is known as a base ISO for their cameras. This is the lowest native ISO setting your camera has. For most cameras today the base ISO is 100. Dig through your camera’s manual and figure out the native ISO. When creating images at this ISO the highest image quality can be attained. 

Most of the time you will be able to create images using the base ISO. However, since it is the lowest ISO setting there are times when you may need to boost the ISO speed to create a proper exposure.

For example, if you are creating images of action, such as flying birds, you will want a fast shutter speed. Typically something faster than 1/1000 of a second. Refer back to the exposure triangle. You have to compensate for the short shutter speed by increasing the ISO and/or opening the aperture.

Star trails are created with a higher ISO and several long exposures stacked together
Star trails are created with a higher ISO and several long exposures stacked together.

When light is minimal the ISO often gets boosted first. Astrophotography is the perfect example. Many star trails and Milky Way images are created with ISO speeds around 3200 or even as high as 6400.

What Is All That Noise?

When film photographers use a higher ISO setting, the emulsion chemistry is larger, creating grain. This is due to the larger particle size of the chemicals. The increased size raises the sensitivity to light and the grain becomes visible.

Increasing ISO raised the potential for digital noise to be introduced into the photo
Increasing ISO raised the potential for digital noise to be introduced into the photo.

A digital camera processes incoming light through the sensor to create an image. When the light is too low, the processing must create pixels. This is essentially the noise you see in a high ISO image. When you raise the ISO, noise appears as graininess or blotchy colors.

Raising the ISO is a creative tradeoff. Determining the correct exposure is one of the joys of photography. If you choose to have an increased ISO you run the risk of bringing in digital noise. And this is fine if the image suits your needs.

For example, if you want a shallow depth of field, the aperture must remain at f/2.8. The subject is moving and to prevent motion blur the shutter speed has to be faster. For these settings, you want to adjust the ISO accordingly.

The left side of this image shows what a high ISO setting looks like compared to a lower ISO on the right
The left side of this image shows what a high ISO setting looks like compared to a lower ISO on the right. Image created by Richard Bednarski.

Most editing software has built-in noise reduction. There are even a few applications dedicated solely to reducing noise. Some even rely on artificial intelligence to reduce noise from a high ISO setting. Topaz Labs creates the most known and widely-used application.

Software is handy and can save an exposure gone wrong. But it is a crutch. Learn how to get the image and exposure correct in the camera. I learned this through film photography. When you master exposure in the camera, post-processing becomes easier and more enjoyable.

Using the native ISO will guarantee maximum image quality
Using the native ISO will guarantee maximum image quality.

Once you master exposure, applications such as Topaz Labs will become tools instead of crutches. Having these tools in your kit will allow you to push your creativity to new levels and grow as a photographer.

Changing the ISO

You need to learn how to change the ISO quickly and without thinking. Having this muscle memory will allow you to create images of spontaneous moments.

Spend some time on the menu of your camera. Most cameras have a specific folder or set for just the ISO. Find a few video guides for your camera. These are helpful because they go over each menu item and what the best settings are for a particular camera. Today’s cameras have a setting for in-camera noise reduction.

In addition, there usually is a dedicated ISO button near the shutter release. Holding this down and toggling a dial will move the ISO up or down. Typically, the ISO adjusts by half a stop; some cameras allow this to be a third of a stop as well.

Practice changing the ISO with your eye looking into the viewfinder. There will most likely be visual feedback in the viewfinder or on the screen letting you know you are changing the ISO. Changing the ISO quickly will allow you to nail a correct exposure more quickly.

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What About Auto ISO?

If you have never calculated exposure, Auto ISO is a good place to start. This allows the camera to determine the best ISO for each exposure.

First, you need to determine the maximum ISO you can tolerate. Remember, the higher the ISO the more digital noise will be present. If your camera is less than three to four years old you can safely cap the ISO at around 3200. Noise is a personnel preference and everyone accepts a varying degree of noise in their images.

Next, you have to tell the camera what the lower ISO setting can be. It is best to set this to your camera’s native ISO. Again most cameras this is ISO 100, refer to your camera’s manual.

The last thing to do is select a minimum shutter speed. If you are using a tripod this is not as important. However, when using only your hands, it is best to use a shutter speed that will avoid camera shake.

Increasing ISO will allow you to use a fast shutter speed and freeze action
Increasing ISO will allow you to use a fast shutter speed and freeze action.

If you are at a sporting event a faster base shutter speed of around 1/1000 will be the best choice, because this will freeze the action. If you are just out on a photo walk the best setting to go with is the reciprocal rule.

Simply take whatever focal length your lens is and put one on top of it (the reciprocal). For example, if you are using a 105 mm lens you would choose a shutter speed of 1/105th of a second. However, since this odd shutter speed does not exist, that correct choice is 1/125th of a second.

A higher ISO will help keep subjects like birds in focus
A higher ISO will help keep subjects like birds in focus.

With these settings in place, you can now go out and create images without worrying about which ISO is correct for the exposure. The camera will do the math for you.

When to Use Auto ISO

The most important time to use auto ISO is when you find yourself in a situation with inconsistent lighting. For example, a client has asked you to create a body of editorial images at an outdoor corporate event. It is outside and clouds are blocking the sun intermittently. This poses a challenge as the light is not always the same.

Or the wedding reception is outside and the couple is moving from the sun to the shade. Or an unevenly lit sports event.

These are all perfect opportunities to select Auto ISO to ensure correct exposure. You will thank yourself when it comes time to edit the images. Each photograph will be relatively evenly lit.

When to Avoid Auto ISO

Auto ISO is a great feature and when used correctly, a tremendous tool. However, it should not serve as a crutch. This means knowing when to use and when not to use it. When working from a tripod and shutter speed is not as critical, using Auto ISO will almost certainly result in a higher ISO speed. This is unnecessary. A slower shutter speed will bring in the additional light needed. Keep the ISO at the native ISO setting.

Likewise, if you are working in a studio setting and have complete control of the light, there is no reason to have the ISO on anything other than the base ISO. Remember, native ISO translates to the highest image quality.

When to Raise the ISO

Below are some common scenarios where you may need to raise the ISO:

  • High-speed subjects, such as an indoor sporting event.
  • Anytime you need a deep depth of field and do not have a tripod, such as in landscape photography.
  • Astrophotography requires a higher ISO speed due to the extremely low light.
  • Portraits in low lighting.
  • Indoor events with limited lighting.
  • Concerts with limited and changing light.
  • Wildlife photography in low light, such as morning or evening.

Choosing the ISO for the Highest Photo Quality

  1. Select which aperture you want. Are you creating a portrait or landscape photo?
  2. Next, set the camera to the native ISO.
  3. With both the aperture and the ISO setting, adjust the shutter speed to create a balanced exposure for your scene or subject. Remember to consider the reciprocal rule. Use a shutter speed that is relevant to your focal length. If this is not possible, consider using a tripod to steady the camera.
  4. Create a test exposure.

If the subject is moving and the chosen exposure results in a blurry subject, slowly raise the ISO. To keep the aperture where you want it, reduce the shutter speed to compensate for the increase in ISO.

This method will guarantee the ISO is as close to the native ISO as possible. If you find the ISO needs to be higher, check your aperture setting. Can you use a wider aperture? Sometimes sacrificing some depth of field is necessary to ensure the greatest image quality and detail.

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Common ISO Scenarios

Here are a handful of examples that provide a reference for choosing an ISO setting. With practice, you will start to see that as the ISO changes the shutter speed is the next setting to change. Do not forget about the aperture.

Macro Photography

ISO:  800

Aperture:  F/4 or lower

Shutter Speed:  1/250

If you do not have a macro light, raise the ISO to around 800 and test your exposure. You want the shutter speed to be around 1/250 a second. Higher if the subject is moving, like an insect or flower in a breeze.

Macro image of a weaver ant
Macro image of a weaver ant.

Sports Photography

ISO:  400 and higher

Aperture:  F/2.8

Shutter Speed: 1/500

If the event is well-lit on a sunny day, you could potentially reduce the ISO to 200. You may have to boost it up to 800 or higher if there are clouds or the event is indoors. You want to keep the shutter speed above 1/500 of a second in order to freeze the motion.

Mountain biker in low light requiring a higher ISO in order to ‘freeze the motion Ebike photo created by freepik www freepik com
Mountain biker in low light, requiring a higher ISO in order to ‘freeze’ the motion. Ebike photo created by freepik – www.freepik.com.

The widest aperture setting on your lens will also be a factor. If it is a fast lens and you can open up to an f/stop of 2.4 or greater, chances are you could lower your ISO. Start with ISO 400 and adjust it to maintain a fast shutter speed.

Landscape Photography

ISO:  100

Aperture:  F/8 or greater

Shutter Speed:  Varies

Keep the camera at the native ISO for the highest quality. Image quality is a defining feature of landscape photography. In order to always use the native ISO, you should be using a tripod. This will steady the camera, allowing you to lengthen the shutter speed in order to get proper exposure.

Landscape image created at ISO 100 using a tripod
Landscape image created at ISO 100 using a tripod. Image created by Richard Bednarski.

Bird Photography

ISO:  1200

Aperture:  F/8

Shutter Speed:  1/1000

Here you want to ensure the shutter speed is as fast as possible. This means raising the ISO to compensate for the lower light entering the camera. Start with ISO 1200 and adjust it lower or higher, depending on the light.

Magnolia Warbler resting on a branch
Magnolia Warbler resting on a branch.

Things to Remember

Knowing how to set the ISO correctly will make you a stronger photographer. Knowing when to use Auto ISO and when to raise the ISO setting will ensure you can work swiftly in fast-paced settings.

Native ISO is the lowest setting a camera is programmed for and creates the highest quality image. You should only raise the ISO if the exposure needs more light. Use a tripod whenever possible to keep the ISO down.

Practice setting exposure in a wide variety of lighting conditions. Spend time working with manual mode. Build muscle memory when setting the shutter speed, aperture, and ISO. These skills will be critical when creating images in a fast-paced situation, such as sports, bird, or event photography.

Frequently Asked Questions

What does ISO stand for?

International Organization of Standardization; is not an acronym and refers to how sensitive film is to light and how much a digital sensor needs to amplify the electric exposure signal.

What is native ISO? 

Native ISO is the lowest ISO speed a camera is programmed to create images. For most cameras, this is usually ISO 100.

What is noise?

Noise is created when using higher ISO speeds, usually anything above 3200. It manifests in the image as digital grain and blotchy colors. Everyone has a different tolerance for noise.

How do I choose an ISO setting?

Start with choosing an aperture setting then select an ISO, and finally select a shutter speed that will ensure a sharp image.

Should I use Auto ISO?

Auto ISO is best used during situations where the light is changing rapidly, such as a cloudy day. Another example is when creating portraits and the subject(s) are moving in and out of shade.

What is the best ISO to use?

While there is no perfect ISO setting, use what is best for the image. Do you want a shallow depth of field? Do you need to freeze motion? Is noise an issue? Think about these variables to help hone your ISO setting.

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