Click to Enlarge MOS-type sensors convert analog information (that is, light) to digital data right on the same chip. In contrast, CCDs -- the sensors used in most digital cameras -- send analog data through a separate circuit board called an analog-to-digital (A/D) converter, then to the camera's image processor, adding noise along the way.
Pentax adopted a Samsung-made CMOS with its new top-of-the-line 14.6-megapixel K20D ($1,300, street, body only), which reaches ISO 6400. "We're able to pack more megapixels on without adding much noise," says John Carlson, manager of product marketing and support at Pentax Imaging Co. "Lower-res sensors create less noise in general. But a CMOS, just by nature of how it processes images, produces less noise."
Still, the K20D produces a fair amount of noise at the highest ISOs compared with other DSLRs we've tested. One reason may be noise reduction, which kicks in as a default setting on many cameras -- but not on the Pentax. "We give photographers control over the amount of noise reduction, and the default is none at all," Carlson says. "So the photographer has the full image information and can apply his or her own noise reduction in editing."
Why not apply it? Noise reduction comes at the expense of resolution and sharpness. Largely due to differences in their image processors, some cameras, such as the Nikon D300 ($1,800, body only), manage to retain a lot of detail even when applying in-camera NR. Others aren't as good at it.
Increasingly sophisticated image processing and camera operating systems have also made a big difference in low-light performance. Not only have the algorithms that control noise improved, but so have those affecting tonal and dynamic range, white balance, color saturation, and other aspects of image quality.
The latest cameras now capture and process image data at a 14-bit color depth, up from 10 bits a few years ago, so that they're handling a much fuller range of tones. The Nikon D3 processes images at 16 bits and writes them to the CF card at either 12 or 14 bits (for NEF RAW files) or the standard 8 bits for RGB-TIFFs and JPEGs.
"Processing image files at a higher bit-depth before reducing them back to a lower bit-depth helps maintain a higher level of quality overall and a smoother gradation of tones in the final image, regardless of file type," says Steve Heiner, senior technology manager, marketing, at Nikon Inc.
Exposure metering also is getting ever more accurate. "In low light, you really have to hit your exposure," says Jay Kinghorn, an Olympus-sponsored pro who used the E-3 for the photo of dancers on the previous spread. "In a scenario like this, with a lot of dark areas that should go to black, you should know how your camera meters and behaves -- and use the histogram to make sure you've got it right."
Then there's autofocus: AF sensors, whether CMOS or CCD, are becoming more sensitive. "The trend is toward more focusing areas, so more of the scene can be considered and moving subjects can be tracked more effectively," says Mark Weir, senior technology and marketing manager for digital cameras at Sony Electronics Inc.
More of those AF points are cross-type, sensitive to both horizontal and vertical lines in the scene. And DSLR makers are adding larger, longer-line AF points, called f/2.8 sensors, designed to work best with faster, wide-aperture lenses, Weir says. While the Sony Alpha 700 ($1,400, street, body only) has just 11 AF points, it clusters many of them, including an f/2.8 sensor, in the center of the field. "This theoretically doubles the AF accuracy of a conventional f/5.6 sensor," he explains.
The Olympus E-3 uses twin cross-sensors arranged in a dense houndstooth pattern that brings in twice as much information to the AF system, says John Knaur. As a result, both AF speed and sensitivity have increased dramatically, particularly with the company's newest lenses, designed to work with the AF system introduced in the E-3.
This trend hit its apex in the Nikon D3 and D300, which have 51 AF points and, tied to Nikon's 3D Color Matrix Metering, a built-in database of 30,000 images. This helps the camera recognize variables such as faces, not just for focus (especially tracking), but for exposure and white balance, which can be hard to determine in mixed light.
In addition, image-stabilization systems now let you shoot handheld at slower shutter speeds, yielding as many as 3 or 4 extra stops before your inadvertent motion blurs the image. How well this works depends not only on the system but on the focal length of the lens -- you'll see a greater advantage with longer telephotos.
Olympus, Pentax, Samsung, and Sony build stabilization into all or some of their DSLRs with systems that shift the sensor in response to your motion -- technology that works with any lens you put on the camera.
On the other hand, Canon, Nikon, Panasonic, and third-party lens makers Sigma and Tamron put the IS system into some of their lenses, but not all of them -- at least, not yet. While stabilized lenses used to cost quite a bit more than their ordinary counterparts, the price difference is diminishing rapidly. And their size and weight is also coming down.
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