One lens to rule them all … that's the dream, isn't it? Imagine, a compact, light L series Canon jobbie with a constant f/1.0, image stabilization, ultrasonic drive and a zoom from 10mm to 400 without distortion. Sigh. While it's probably not all that far away, for the meantime we have to put up with constantly switching lenses to get the effects we're after. And if we want a bit of extra length on our telephoto lenses, we can always put an extender on it.

Of course, an extender is twice as fiddly to switch on as a lens ... remove the zoom lens, get out your doubler, pull the caps off both ends of it, attach it to the lens, then stick it back on the camera.

Which is what makes this new lens from Canon such a sweet idea – it's a super-long 200-400mm telephoto zoom with a built-in 1.4x focal length extender that kicks in at the flick of a switch.

So it's effectively two lenses in one – a 200-400mm and a 280-560mm zoom, both with a constant f/4 maximum aperture. If you stick it on a 1.6x crop frame APS-C sensor camera like Canon's 7D, that means you've got a zoom that can cover anywhere between 320-896mm equivalents on a full-frame camera. Visit the Vatican for Sunday mass and you'll be counting blackheads on the Pope's nose.

This new monster's official designation is the Canon EF 200-400mm f/4L IS USM EXTENDER 1.4x. It should be every bit as well-made as the rest of Canon's L series – meaning that it'll be waterproof, sturdy and responsible for hefty chiropractor's bills.

It's got three image stabilization options, which will be vital for such a long zoom at a decent but not super-quick f/4.0. Canon is pitching it at sports and wildlife photographers – presumably very wealthy ones, as anyone who has looked at price lists for longer L series zooms will attest.

Great idea though, and wouldn't it be great to start seeing extenders (or wide-angle adapters) built in to other popular lenses in the Canon stable?

Look for this lens to hit the market some time in 2011, after seeing its first trade show at CP+ in Yokohama in the next few days.