The High ISO Challenge – David Yeoman

Many of us look at images taken in low light, and admire the photographic techniques used, and wish we could take shots like that.

Digital cameras react to light, each pixel on the sensor is effectively a well, and as the shutter opens, the well fills with light (if it makes it easier think of beer being poured into a glass!). In low light if the shutter is only open for a relatively short time, then only a little bit of light gets in.

Increasing the ISO artificially increases the amount of light in the well by applying gain.  Doubling the ISO multiplies the amount of light (or beer poured!) by two. This gain increase unfortunately doesn’t come for free, the multiplication function isn’t perfect and it’s action introduces noise (the digital equivalent of film grain).

In the early day’s of the digital camera, manufacturers really struggled to keep the amount of noise under control, but as sensor technology improved, the impact of the noise has been reduced. It’s still present though, but today’s cameras are way better in lower light.

There are some laws of physics to be applied here, the bigger the opening to the well, the better the noise is controlled. Going back to the beer example, imagine 4 pint glasses in a line and a large jug of beer, if you try to pour the beer in a fixed time (say 5 seconds) across the line of glasses in order to get the same amount in each glass, it’s a lot easier and a lot less messy than if you tried the same with 8 half pint glasses!

So lower pixel density sensors are better at higher ISO. Now actually that’s not quite true, it should read lower density sensors of the same comparable technology and physical size will be better in lower light. The latest high pixel density sensor often works better than previous generation lower density sensors.

The noise manifests itself as Luminance (brightness) and Chroma (colour) noise, and this noise has both magnitude and a spatial frequency. This noise is what we try to clean up to make our images acceptable.

Understanding how to set the camera up, to minimise the resultant image noise is the key to getting good results from High ISO shooting. This then presents less ‘noise’ that we have to clean up in post processing (or the camera processing has to clean up if shooting JPGs). These techniques are applicable to any Fuji X camera, and the use of them will result in cleaner images.

The latest Fuji X-Trans3 sensors were a significant step forward in shooting high ISO images, although the initial reviews suggested only a small gain in High ISO capability, the way that the noise manifests itself in real world situations, means that there is a significant improvement in the final result.

Shooting at High ISO is one of methods we will use on the Fujiholics Low Light Techniques Workshop, the first of which will be held in Liverpool on 21st April 2018. The workshop will be hosted by David Yeoman. David has over 25 years digital camera experience in an industrial imaging environment where he designs and implements automated inspection systems for clients. His vast technical knowledge allows him to explain in easy to understand terms the operation of camera. He has over 5 years experience with X series cameras and currently shooting the X-T2 and X100F.

To view David’s work please click this link:

Manchester Urbanscapes with David Yeoman

Also

Liverpool Dusk into Night with David Yeoman

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