Bob Atkins has published a short, technical guide to digital sensor size, looking at several digital cameras with different physical sensor sizes but all with a nominal 3 megapixel (3MP) pixel count.

”“So what” you might think, “if you have enough pixels, what does the sensor size matter?”. Cameras with smaller sensors use shorter focal length lenses to get the same angular coverage as cameras with larger sensors do with longer focal length lenses. So if you have a 28-105mm zoom on a Canon D30,  a 10-37mm zoom on a Nikon 995 or a 7.4-28mm zoom on a Minolta Xi, you get approximately the same shot. What’s the big deal about the physical size of the sensor? Why does it matter?”

Website: Bob Atkins - Digital Sensor Size - Why Size Matters