Understanding ISO. Photography for beginners

Every picture you ever take will involve ISO, aperture and shutter-speed. ISO is a key part of the three but should be the last you mess with.

It is extremely hard to take good pictures without a good understanding of how ISO works and what it does. Camera ISO is one of the three pillars of photography (the other two being Aperture and Shutter Speed) and every photographer should thoroughly understand it, to get the most out of their equipment.

What is ISO?

Your ISO allows you to take pictures in low light situations.

It is basically a measure of your digital sensor’s sensitivity to light. The higher the number, the more sensitive to light your sensor becomes.

ISO Speed & Noise

However, all this increase in sensitivity does not come free. There is a price to pay with your image appearing more noisy.

See, when you boost the sensitivity of your image sensor by selecting a higher ISO, the image sensor is now able to record a fainter light signal. However, it is also true now that it will record fainter noise, where noise is any signal that is not attributed to the light from your subject. Remember that an image sensor is still an analog device and it generates its own noise, too! The increased sensitivity allows the image sensor to record more light signal and more noise. The ratio of light signal to noise (S/N ratio) determines the “noise” in your resultant image.

An image sensor is usually calibrated so that it gives the best image quality (greatest S/N ratio) at its lowest possible ISO speed. For most consumer digital cameras, this value will be expressed as ISO 50, ISO 64 or ISO 100. A few digital cameras use ISO 200 as their lowest ISO speed.

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The lower the ISO the less noise you will see. As your ISO increases, the noise level does as well. This noise level most likely will not become significant until your ISO reaches numbers of 800 or higher (depending on your camera).