What is ISO?
To start at the beginning, ISO stands for International Organization of Standards. It sets the standard for measuring the sensitivity of camera sensors. It dates back to the film days when it referred to the film’s speed or, as it was called then, ASA which stands for American Standards Association.
Films had a fixed ISO. To change the ISO, you had to load a different film in your camera. Digital cameras can change the ISO whenever it is needed. This is a huge advantage as the digital photographer can instantly respond to changing light conditions.
What Does Changing the ISO Do?
Changing the ISO increases or decreases the sensor’s sensitivity. What that means is when the sensor is set at a low ISO it is less sensitive, requiring more light go get a proper exposure. When set at a higher ISO it is more sensitive, requiring less light to get a proper exposure.
In most cameras the lowest ISO is 100. With the advancements that have been made in recent years, it’s common to see the high ISOs around 12,800.
The ISOs are laid out in f/stops or Exposure Values (EV). These measures are based on doubles or halves. Doubling the ISO from 100 to 200 doubles the sensitivity resulting in needing half the amount of light to get a proper exposure. Increasing the ISO from 100 to 400 quadruples the sensitivity resulting in the amount of light needed for a proper is reduced by 4.
How Does ISO Work in a Digital Camera?
The technology that allows us to change ISOs has gotten very sophisticated. And different sensors (CMOS vs CCD) employ different technologies. Part of the ISO increase is by increasing the voltage to the sensor. This can occur in the sensor itself or outside the sensor. The signals coming out of the sensor need to be converted from analog to digital and in some cases additional ISO boost is done to the digital signal. The engineering that goes into this is highly sophisticated as I’m sure you can imagine.
What Are the Effects of Using High ISOs?
Lower ISOs produces higher quality images. Most landscape photography is shot at ISO 100. Higher ISOs make it possible to shoot in low light conditions, but they run the risk of increased noise, especially in the shadows. Noise manifests itself in a way that is similar to grain in high ISO films. It produces a blotchy look.
But the technology has progressed so far that ISOs in the 800 to 1600 range that were unthinkable just a few years ago now produce excellent results. And one can expect the situation to only get better. This is great news for night photographers.
Summing It Up
Most landscape photography can be shot with the lowest ISO, especially when using a tripod. However, higher ISOs are available for tricky low-light conditions and can be used with confidence.
Exposure Triangle
ISO is one of the three sides of the Exposure Triangle. It works in conjunction with aperture and shutter speed to get a proper exposure.
The sides of the exposure triangle are measured in stops. The ISO determines how much light is required to get a proper exposure. An ISO of 100 requires twice as much light as ISO 200.
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Read more:
Tell Me More About Exposure
Tell Me More About Aperture
Tell Me More About Shutter Speed
Tell Me More About the Exposure Triangle
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