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There’s another, even more basic, reason why the mere number of pixels is not the only issue. If you have two sensors of the same physical size, one with six megapixels and one with 12, it’s obvious that the individual pixel-sites on the 12mp sensor are going to be smaller; each will only have half the area, which means it can only collect half as much light. This may not matter too much when there’s loads of light around, but that’s not always certain in the great outdoors.

This indicates that we should be less obsessed with pixel numbers and more concerned with pixel size. Pixel size is determined by the number of pixels and the size of the sensor. However, while the pixel number is plastered all over advertising and packaging, you’ll usually have to dig deeper for any information on sensor size.

So here it is in a nutshell:

 SLR-type camera: big sensor

 Compact camera: small sensor

 Mobile phone camera: teeny tiny sensor.

There are variations within each category – for more information, see under ‘camera types’, below – but very crudely, SLR sensors are somewhere in the postage-stamp size bracket. Compact camera sensors are smaller than your smallest fingernail. And cameraphone sensors are so small you can barely see them.