Camera Basics #5: ISO Speed

ISO speed plays an equally important role as aperture and shutter speed in its effect on exposure. Now let us learn more about the advantages and disadvantages of turning up the ISO speed.

In a low light environment, we can increase the shutter speed by turning up the ISO speed


– Within Normal ISO speed range, the lower the ISO speed, the higher the image quality.
– Increasing the ISO speed allows the camera to set a faster shutter speed.
– Noise occurs at higher ISO speeds.

To put it simply, ISO speed is the image sensor’s capability to sense light, reflected as a numerical value. It is said that exposure makes or breaks a picture, but ISO speed is also a major factor in determining exposure.

If aperture is the width of the light ray passing through and shutter speed is the time taken for the light ray to pass through, then ISO speed describes the image sensor’s capability in sensing light. The higher the value, the more sensitive the camera to light. Even under dark environments or when taking pictures of night scenery, we can still take good, bright pictures. In other words, assuming that we don’t need the image to be brighter, a higher ISO speed makes a faster shutter speed possible. Simply by adjusting the ISO speed, we increase the shutter speed. By doing so, we can prevent the blurring that results from camera shake or subject motion blur.

A higher ISO speed also allows us to achieve a narrower aperture without compromising on image brightness, as long as we use a fixed shutter speed (such as by using Shutter-priority AE mode).

As much as I am saying that ISO speed is such a useful function, it has its disadvantages too. The higher the ISO speed, the more noise it generates. The overall image comes up grainy. Yes, there are cameras with noise reduction features around, but most photographers will still try their best keep the ISO speed to a setting that does enough to prevent blurring from camera shake. Usually, this is as close to the base ISO speed (lowest Normal ISO speed) as possible, but may be higher depending on photographic intent and shooting conditions.

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