Psst, get closer with a 12x digital camera

A large range of focal lengths to zoom through can dramatically increase your framing options, as well as simply make it possible to get recognizable people shots when you're trapped in the crowd, high in the bleacher seats, or at the back of the auditorium. See how these stabilized 12x zoomers stack up.

Like high resolution, the term megazoom is a moving target: 6x, 7x, 8x, 10x, and now 12x. Unlike the current crop of so-called high-resolution cameras, however, large zoom ranges confer clear, tangible benefits. Though many pro photographers eschew the long focal-length lens and zoom with their feet, we don't all have the luxury or comfort level for in-your-face photography.

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	Canon's EF 100-400mm F4.5-5.6L IS USM

That's why digital SLRs, with their interchangeable lenses, are so appealing and why you have to pay close attention to the maximum aperture available on any megazoom lens. The Leica lens on Panasonic's models support an aperture of F2.8 throughout the zoom range; that's not very impressive at 36mm, but when you're shooting at 432mm, it gives you more available-light latitude than Canon's F3.5 or Sony's F3.7--about two-thirds of a stop.

Second, physics dictates that as you increase the focal length, something's gotta give to decrease the amount of light that scatters relative to the amount that focuses: The aperture has to shrink, the shutter speed has to increase, camera motion must decrease, or sharpness gets sacrificed. In practice, you can't shrink the aperture too much without falling over the other side of the curve, where the negative effects of diffraction start to overwhelm the positive effects of the smaller aperture--or you simply run out of light.

That's where you see all sorts of artifacts, such as distortion and fringing. Increasing the light sensitivity by upping the ISO setting has the same effect as changing the aperture or shutter speed, but increases visual noise. A tripod decreases the motion but that's not always a practical solution. And nobody wants a blurry photo. So traditionally, photographers have compensated by increasing shutter speed: Optimally, you should never shoot at a shutter speed slower than the reciprocal of the focal length (in other words, 1/F). But that's not always feasible either, especially when you hit extreme telephoto territory, such as 400mm.