Image copyright Ben Birchall
Shooting indoor sports action using a fast shutter speed, old, gloomy churches without flash or bright landscapes where you want to slow down the shutter speed to capture movement are just some of the many situations where you will need an extreme ISO to get better results.
ISO denotes how sensitive an image sensor is. Any change from the manufacturer’s native ISO (the lowest default, which produces the optimum image quality) will have some form of electrical signal modification that results in noise.
Most DSLRs have a native ISO of around 100 or 200; beyond that, at the extreme low end of the range, quality isn’t improved. However, some manufacturers offer lower ISO values in the menu, such as ISO 50. Others use a decimalised f-stop value to indicate when it falls below the native ISO.
Both are great for using wide apertures (for more on apertures, download our free f-stop chart for understanding aperture) or long shutter speeds in bright lighting conditions.
When using extreme ISO values above the highest setting, most cameras share the prefix letter H followed by an f-stop value to indicate when the ISO is being ‘pushed’ to the limit. Such images can be very noisy, but will allow you to carry on shooting in very dark conditions.
Step 1: Go manual
Turn off any ISO sensitivity control modes that automatically select a suitable ISO depending on the shutter speed and aperture. You should also switch off any Scene modes and select either Manual or
a semi-automatic exposure mode.
Step 2: Select the ISO
Most recent cameras will have a dedicated ISO button that’s located on the camera body. Locate the button on your camera and have a scroll through the ISO values from one end to the other to see if you have the L or H prefix.
Step 3: Reduce the noise
Any amplification or reduction of the electrical signal that’s been produced by light falling on the sensor’s CCD will suffer from noise. Dig into your DSLR’s menu and turn on any in-camera noise reduction for the very best results.
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