What is ISO sensitivity? Understanding Its Relationship with Exposure and Examples of Settings

For those just starting with photography, the term "ISO sensitivity" may seem unfamiliar. However, understanding ISO sensitivity will give you a deeper knowledge of exposure and how to control it. This article introduces the basics of ISO sensitivity and provides detailed examples of settings for various scenes.

ISO sensitivity, F-number, and shutter speed

In digital single-lens reflex cameras, exposure is adjusted using three elements: the F-number (aperture), shutter speed, and ISO sensitivity. The amount of light entering the sensor is changed by the F-number and shutter speed, and the light is amplified by adjusting the ISO sensitivity. By raising the ISO sensitivity, you can maintain the same brightness even if you reduce the F-number or increase the shutter speed.
Typically, when shooting in auto exposure mode, the camera adjusts the F-number and shutter speed, leaving ISO sensitivity to be set to automatic.

What is ISO sensitivity?

ISO sensitivity (often just called ISO) is a numerical value that represents how sensitive a camera’s image sensor is to light. A higher number means that the light signals are amplified, allowing for brighter photos in low-light environments. ISO 100 is the base value, and when the number is doubled, it is referred to as "1 stop increase" in sensitivity. For example, ISO 100 increases to ISO 200, and half the amount of light is needed to achieve the same exposure.
However, setting ISO sensitivity too high can cause visible background noise, reducing image quality. It is important to adjust the ISO while keeping an eye on the final result of your photo.

Scenes suitable for lower ISO sensitivity

In bright environments, it is recommended to set ISO sensitivity lower. Lower sensitivity helps reduce noise, making it easier to achieve clearer, high-quality images. For scenes where you want to capture sharp details, such as nightscapes, landscapes, or architectural photography, it is a good idea to start with a lower ISO sensitivity. Additionally, if you're using a tripod, you can prevent camera shake and often shoot with low ISO and slower shutter speeds.

Scenes suitable for higher ISO sensitivity

In low-light conditions or situations that require fast shutter speeds, increase the ISO sensitivity. This allows you to capture brighter images even when less light is available.
For example, when you need a fast shutter speed to prevent camera shake or when you cannot use a flash, increasing the ISO sensitivity will help. However, as mentioned earlier, increasing the ISO sensitivity too much may cause noticeable noise, so be mindful not to set it too high.

Examples of ISO sensitivity settings for different scenes

The appropriate ISO sensitivity varies depending on the shooting scene. Here, we introduce examples of ISO sensitivity settings for various situations and explain how to effectively use ISO in each scene. However, these settings are just guidelines, so be sure to adjust based on the actual results of your photos.

Outdoor in sunny weather

On a sunny day outdoors, the abundant light allows you to shoot with ISO sensitivity between ISO 100 and ISO 400, which will provide sufficiently bright photos. Using a lower ISO sensitivity will help produce clearer images. This setting is ideal for capturing landscapes, architecture, or any scene where you want to capture fine details.
However, for scenes such as backlit photography, exposure compensation may be needed to avoid highlights or shadows being overexposed or underexposed.

Outdoor on cloudy days

On cloudy or drizzly days, where the light may be insufficient, setting the ISO sensitivity between ISO 400 and ISO 800 is ideal. This will help you maintain the correct exposure while keeping the F-number and shutter speed in a reasonable range.
Additionally, the soft light on cloudy days can provide a gentle effect, which works well for creating a soft mood for the subject. If you're shooting after rain, setting the ISO slightly higher can help emphasize a moist, fresh atmosphere.

Indoor photography

If natural light or bright light sources are available indoors, a lower ISO sensitivity is often sufficient to achieve bright photos. However, if you are further from the window or have weak light sources, setting the ISO sensitivity between ISO 800 and ISO 3200 is a good starting point. When shooting handheld, aim for a shutter speed of 1/60 seconds or faster to prevent camera shake.

Night photography

For night photography, use a tripod and set the ISO sensitivity between ISO 100 and ISO 400. A low ISO setting will help you capture clearer images with minimal noise. You can also use long exposure to capture beautiful light trails and details in the scene.
If you want to emphasize the texture or atmosphere of the lights, you might increase the ISO sensitivity. Adjust the ISO based on the brightness of streetlights or building lights.

Starry Sky photography

For photographing starry skies, the typical ISO sensitivity setting ranges from ISO 1600 to ISO 6400. Using a high ISO sensitivity allows you to capture the faint light of the stars. However, be aware that high ISO sensitivity may introduce noise, so balance it with the desired image quality.
Also, the sky’s brightness will change based on the season and the moon's phase, so adjust the ISO sensitivity accordingly.

Sports or athletic events

In sports photography, where subjects move quickly, you need a fast shutter speed. To ensure proper exposure with a fast shutter speed, setting the ISO between ISO 800 and ISO 3200 will make this possible.
In indoor arenas, where light may be insufficient, you may need to set the ISO even higher. Conversely, on a sunny day outdoors, a relatively lower ISO sensitivity of ISO 400 to ISO 800 will allow you to maintain fast shutter speeds while getting the correct exposure.

Recommended TAMRON lenses

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Adjusting exposure with ISO sensitivity

ISO sensitivity plays a significant role in exposure. By setting the appropriate ISO sensitivity for the scene or subject, you can achieve the desired exposure. Challenge yourself to experiment with different scenes and subjects while developing your sense of how aperture, shutter speed, and ISO sensitivity affect the final image.