This is a way of increasing a camera’s apparent zooming ability by enlarging the central part of the image captured by the sensor. It’s a ‘cheat’ that’s worth very little.

Even so, makers often describe a camera’s ‘digital’ zoom as if it’s an extension of its optical zoom. Indeed, on many cameras if you keep the zoom button pressed past the point where it reaches its maximum optical zoom, it swaps to the digital zoom automatically.

As this diagram shows, however, digital zooms work by simply blowing up the central part of the image captured by the sensor. It looks like you’ve zoomed in further, but in fact all that’s happened is that the middle part of the picture has been cut out and blown up.

Makers will often introduce impressive-sounding technologies which make it harder to figure out exactly what’s going on, but they still boil down to the same thing. For example, this is what Panasonic says on its website about the Lumix TZ10:

“Furthermore, the Extra Optical Zoom function that extends zoom power to 23.4x (at 3-megapixel resolution) by using the center part of the large CCD to bring subjects even closer.”

Now if it’s using the centre part of the CCD, and the resolution is reduced, that sounds like a perfectly standard digital zoom. So where does the ‘Extra Optical Zoom function’ come from?

Digital zooms are worth using only if you’re prepared to accept the lower resolution in exchange for a tighter crop on your main subject. But if you find you’re using the digital zoom often, you’d be better off swapping your camera for one which has a longer optical zoom range.