What Does ISO Stand for in Photography? Understanding ISO for Beginners - A Guide

ISO in photography is an important setting to understand for every shooting situation.

ISO in photography relates to shutter speed and aperture by affecting the camera’s sensitivity to light, allowing for adjustments to be made to achieve proper exposure while maintaining desired shutter speed and aperture settings.

What Does ISO Stand for in Photography?

What does ISO mean?

ISO stands for International Organization for Standardization, and in photography, it refers to the sensitivity of a camera’s image sensor to light.

ASA or ISO in Old Film Cameras

Old film cameras may have their film speed set using ASA or DIN. ASA (American Standards Association) was the organization that existed before it was merged into the International Organization for Standardization (ISO).


ISO, ASA, and DIN are all different standards used to measure the sensitivity of photographic film or image sensors in digital cameras. The ISO standard is the modern equivalent of the older ASA and DIN standards, with ISO being the internationally recognized standard for measuring the sensitivity of film or digital camera sensors.

What is ASA in Photography?

ASA (American Standards Association) in photography refers to a system of measuring the sensitivity of photographic film to light. It was later replaced by ISO (International Organization for Standardization) as the standard measurement for film sensitivity. It is determined by measuring the amount of light required to create a particular level of density on the film.

What is DIN in Photography?

DIN is a measure of the sensitivity of photographic film to light, similar to the ASA or ISO rating. It stands for Deutsches Institut für Normung, the German national organization for standardization.

The DIN rating is another way to measure film speed in photography, and it is closely related to the ISO rating. In fact, the DIN rating is simply the ISO rating multiplied by 3.32. For example, ISO 200 film would have a DIN rating of approximately 24.

ISO in Modern Cameras DSLRs and Mirrorless

In a digital camera, ISO refers to the camera’s sensitivity to light. It is a measure of how much amplification the camera applies to the signal from the image sensor to increase its brightness.

When the ISO in a digital camera is increased, the camera’s sensitivity to light is also increased, allowing for better performance in low-light conditions or faster shutter speeds, but at the cost of increased digital noise, which can result in reduced image quality.

How ISO Works

The photography exposure triangle refers to the relationship between aperture, shutter speed, and ISO. ISO is one of the three factors that determine exposure, with the other two being aperture and shutter speed. By adjusting the ISO, the sensitivity of the camera’s sensor to light is changed, which affects the overall exposure of the image.

ISO can be increased in a dark environment to allow for a faster shutter speed and/or smaller aperture, which can help to capture a properly exposed image in low light conditions without the need for additional lighting equipment. However, increasing ISO can also introduce digital noise into the image, so it is important to find a balance between ISO, shutter speed, and aperture to achieve the desired result.

The Exposure Triangle and ISO

Shutter speed, aperture, and ISO are the three elements that make up the exposure triangle in photography. Shutter speed controls the duration of time that light enters the camera, aperture controls the amount of light that enters the camera, and ISO controls the camera’s sensitivity to light. Together, these elements determine the exposure of the image.

When the aperture is increased (i.e., the f-stop number is decreased), more light enters the camera, which means the exposure is increased. To maintain the same exposure, either the shutter speed can be increased (shortened) or the ISO can be decreased.

When the aperture is decreased (i.e. made smaller), less light enters the camera and therefore the exposure is reduced. To compensate for this reduction in exposure, either the shutter speed needs to be decreased (i.e. made slower) or the ISO needs to be increased (i.e. made more sensitive to light).

When the shutter speed is increased, the amount of light entering the camera is reduced, so either the ISO or film speed needs to be increased to compensate and maintain the correct exposure.

Image Quality Noise from High ISO Settings

ISO plays a significant role in determining the image quality or noise in a digital photograph. The higher the ISO setting, the more sensitive the camera sensor becomes to light, resulting in brighter images with less exposure time. However, this can also result in an increase in the amount of image noise, which appears as grain or color distortion. Therefore, finding a balance between ISO, aperture, and shutter speed is crucial to producing high-quality images with minimal noise. Additionally, newer camera models often have better noise reduction technology that can help reduce the impact of high ISO settings on image quality.

Here are some techniques that can be used to reduce image noise from shooting at a high ISO:

  1. Use the lowest possible ISO: Set the ISO to the lowest possible value that still allows you to capture a properly exposed image.

  2. Increase the amount of light: Add more light to the scene by using a flash, opening blinds or curtains, or using a reflector.

  3. Use a larger aperture: A larger aperture (smaller f-number) will allow more light to enter the camera, which can reduce the need for a high ISO.

  4. Use a slower shutter speed: Slowing down the shutter speed can allow more light to enter the camera, but be careful not to use a shutter speed that is too slow and results in camera shake.

  5. Use noise reduction software: There are several software programs available that can help reduce image noise in post-processing.

  6. Use a camera with good high-ISO performance: Some camera models are better at handling high ISOs than others, so choosing a camera with good high-ISO performance can help reduce image noise.

Native or Base ISO

The base ISO, also known as the native ISO, is the lowest ISO setting at which a camera’s sensor can capture light without any amplification or digital manipulation. At the base ISO, the sensor’s full dynamic range is available, resulting in the highest possible image quality with the least amount of noise.

Here’s a list of the base ISO for different sensor sizes:

  • Micro Four Thirds: ISO 200
  • APS-C: ISO 100
  • Full Frame: ISO 64-100
  • Medium Format: ISO 50-64

Please note that these values can vary between different camera models and manufacturers.

What is Extended ISO?

Extended ISO refers to ISO values that are artificially created by the camera, usually beyond the native ISO range of the sensor, in order to increase or decrease sensitivity beyond the normal range. These extended ISO settings can lead to increased noise or reduced dynamic range in the image.

ISO for Landscape Photography

The best ISO to shoot at for landscape photography varies depending on the lighting conditions and the specific camera being used, but generally the base ISO is preferred as it will allow you to achieve optimal image quality with the lowest amount of noise.

The ISO setting to use for landscape photography during golden hour would depend on the lighting conditions and the aperture and shutter speed settings that are desired. Typically, a lower ISO setting between 100-400 would be ideal to achieve high image quality and capture fine details in the landscape during the soft, warm light of golden hour. However, it may be necessary to increase the ISO setting if a faster shutter speed or narrower aperture is needed to capture a particular shot.

ISO for Nighttime Photography

The ISO for nighttime photography can vary depending on the available light and desired exposure. Typically, a higher ISO is used to capture more light in low light situations, but this can also introduce more noise to the image. A range of ISO values from 800 to 3200 may be used for nighttime photography. It’s important to experiment with different ISO settings to achieve the desired effect for a specific shot.

For nighttime photography, a lens with a wide maximum aperture (low f-number) is typically preferred to allow more light to enter the camera and compensate for the low light conditions. This type of lens is often referred to as a “fast” lens. A prime lens (fixed focal length) with a maximum aperture of f/1.4, f/1.8, or f/2 is a popular choice for nighttime photography.

Here is a list of the kinds of photography people do at night:

  • Cityscape/Architecture Photography
  • Night Sky Photography (Stars, Milky Way, etc.)
  • Light Painting Photography
  • Fireworks Photography
  • Astrophotography
  • Nighttime Landscape Photography
  • Street Photography
  • Concert and Event Photography
  • Nighttime Wildlife Photography
  • Nighttime Sports Photography

ISO for Portrait Photography

The ISO for portrait photography can vary depending on the available light, desired depth of field, and the desired level of noise in the image. In general, a lower ISO is preferred to minimize noise, especially for studio portraits with controlled lighting.

A range of ISO 100-400 is commonly used for portrait photography, but higher ISOs may be necessary in low light situations or for capturing action in outdoor portraits. Ultimately, the ISO setting should be adjusted in conjunction with shutter speed and aperture to achieve the desired exposure and creative effect.

ISO for Street Photography

The recommended ISO for street photography can vary depending on the lighting conditions and desired aesthetic, but generally, a lower ISO is preferred to maintain image quality and reduce noise.

During daytime street photography in good lighting conditions, a low ISO of 100-400 is recommended to ensure the best image quality. However, in low light situations such as night time street photography, a higher ISO of 800-3200 may be necessary to achieve a proper exposure. It’s important to balance the ISO with the shutter speed and aperture settings to ensure a well-exposed and sharp image.

ISO for Wildlife Photography

The ISO for wildlife photography can vary depending on the lighting conditions and the behavior of the animals. In general, it is best to use the lowest possible ISO to achieve the desired shutter speed and aperture for the shot. This can help to minimize noise and maximize image quality.

However, in low light conditions, a higher ISO may be necessary to maintain a fast enough shutter speed to freeze motion and avoid blur. In such cases, using a camera with good high-ISO performance can be helpful. Wildlife photography often requires a long telephoto lens, which typically has a narrower maximum aperture, so using a higher ISO may be necessary in order to maintain a sufficient depth of field.

When shooting wildlife, it’s important to use a fast enough shutter speed to freeze motion and avoid blur caused by the animal’s movements. A good rule of thumb is to use a shutter speed that is at least equal to the focal length of the lens (in 35mm equivalent) to minimize camera shake and motion blur.

For example, if you are using a 300mm lens on a full-frame camera, you should use a shutter speed of at least 1/300th of a second. If shooting in low light, you may need to increase the ISO to maintain a fast enough shutter speed.