26 Nov The High ISO Challenge – David Yeoman

Source: Fujiholics

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!

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