6. ISO Rating
If you've ever wondered what that 'ISO' option in your FinePix menu was, or why Fujifilm makes so much fuss about the high ISO capabilities of cameras of these and other similar cameras, then read on...
ISO is a measure of how sensitive your camera's sensor (or film, which is where the ISO system was first adopted) is to light. The higher the ISO number the more sensitive the sensor is, and therefore the lower the amount of light needed to make an acceptable picture. Put simply, higher ISOs allow you to take pictures in lower light, or, more accurately, to take pictures in lower light without needing long exposures, which would result in camera shake.
In the days before digital cameras' sensitivity was defined by the film – you bought an ISO 50 (low sensitivity) film for bright weather, and maybe an ISO 400 or 800 film for dull days or night photography, or for specialist applications such as sports, where a high shutter speed is essential. Digital cameras allow you to do something film never did – to change the ISO setting from shot-to-shot, according to your needs.
So why not just use the highest sensitivity setting all the time? Surely that would be a sensible approach to avoiding camera shake in every situation? Not so. There are a couple of very good – and totally unrelated - reasons for having the option to change the ISO setting. The first is versatility; high sensitivity means you need very little light to get the right exposure, meaning creative techniques such as limiting depth of field by using a very wide aperture, or using long exposures to capture motion, would prove difficult. Sometimes you simply don't want the camera to be that sensitive to light!
The second reason is image quality. Digital camera sensors (the 'CCD') are not very sensitive to light, and most have an 'optimum' ISO setting of ISO 80 or even less.