An image sensor produces the best signal-to-noise ratio when as much light hits it as possible, short of causing pixels to blow out—and the higher the signal-to-noise ratio, the better the image quality, not just in terms of noise, but in terms of dynamic range, color and even resolution (as noise adversely affects all of these things). With higher ISO settings, less light hits the sensor; that's the whole point of higher ISO settings—to let you use faster shutter speeds and/or smaller apertures in a given light level—and the less light that hits the sensor, the worse the signal-to-noise ratio and, thus, the worse the image quality. But the newer sensors combined with more powerful image processors have better noise-reduction algorithms and produce better image quality at higher ISOs than ever before. The Canon EOS-1D X and Nikon D4 should provide the best results, yet at higher ISO settings. No, you're not going to get stunning results at their ISO 204,800 top setting, but we'd expect ISO 12,800 and even higher to produce very usable images with these cameras—and even that's incredible!
With their much smaller APS-C sensors, the Sigma SD1 and Sony SLT-A77 can't be expected to do as well at higher ISO settings as the full-frame EOS-1D X and D4, but they do better than one might expect, thanks to improved onboard processors, as well as their image sensors.
Best known as a lens manufacturer, Sigma also has produced a line of DSLRs and compact digital cameras, all featuring the unique Foveon X3 "full-color" image sensor. The new SD1 is Sigma's first pro DSLR. As we went to press, Sigma announced that the SD1 will be renamed the SD1 Merrill, and the price will be changed to $3,300 MSRP.
The Sigma System. As a lens maker, Sigma offers a selection of more than 40 for the SD1, from a 4.5mm circular fisheye and an 8-16mm superwide zoom to an 800mm supertelephoto, including macro lenses. With the SD1's 1.5x focal-length factor, this gives users access to focal lengths equivalent to 12mm to 1200mm on a 35mm camera (not counting the circular and full-frame fisheyes). A number of the lenses offer OS optical stabilization, and teleconverters of 1.4x and 2x are available.
Built-In Flash. Few pro DSLRs have a built-in flash unit, but the SD1 has one (ISO 100, GN 11, in meters, covers the field of view of a 17mm lens). There's also a PC connector for studio flash systems. Maximum flash-sync shutter speed is 1⁄180 sec.
No Need For A Low-Pass Filter. Because each pixel site records all three primary colors, there's no need for an RGB filter grid, demosaicing or a resolution- and sharpness-robbing low-pass filter. As a result, the Foveon sensor delivers a resolution equivalent to that of a conventional sensor of a somewhat higher pixel count. Exactly how much more is subject to debate.
Rugged, Sealed Body. The SD1 is Sigma's first pro body, featuring rugged, yet lightweight magnesium-alloy construction. It's splash-proof and dust-resistant, with a shutter tested to more than 100,000 cycles. A lens-mount dust protector doubles as the camera's infrared filter.
Dial-Driven Mode Selection. Operation is straightforward. Twin control dials provide direct access to exposure modes (program, shutter-priority, aperture-priority and metered manual), drive modes and user-chosen custom settings. You even can activate mirror prelock without going into LCD monitor menus.
AF & Metering System. The 11-point AF system with twin cross-sensors allows you to select any point (or let the camera do it). It works in conjunction with the 77-segment evaluative metering system (which also provides center-weighted, 10% central and 1% and spot capability).
Viewfinder And LCD. Composing is done via the eye-level SLR pentaprism finder, which shoots 98% of the actual image area at 0.95x magnification. A 3.0-inch, 460,000-dot LCD monitor makes it easy to review images (but there's no Live View mode).
Foveon Sensor. At the heart of the SD1 is its Foveon image sensor, this one featuring 3 times the pixel count of previous Sigma DSLRs, which, Sigma states, allows it to compete not just with high-end DSLRs, but with many medium-format digital cameras. While conventional image sensors—those used in all other DSLRs—record just one primary color (red, green or blue) at each pixel site, the Foveon records all three colors at every pixel site. Because it doesn't have to interpolate missing colors at each pixel site, the Foveon sensor also delivers a unique color rendition. Sigma's TRUE II (Three-layer Responsive Ultimate Engine) image processor optimizes output from the X3 sensor.