Sigma SD9 Digital SLR review: Sigma SD9 Digital SLR

The Sigma SD9 works far better as a proof of concept for the Foveon X3 sensor it uses than as a practical digital SLR. The first camera to take advantage of Foveon's 3.42-megapixel, 10.3-million photodetector imager, the SD9 manages to capture extremely sharp images of stationary or slow-moving subjects in good light. But action and low-light scenes produce mixed results, and when combined with the rest of this camera's characteristics, it all adds up to a mediocre digital SLR that displays flashes of greatness only occasionally.

Sigma clumps one set of controls on the top left of the camera.

With its monotone matte-black finish and boxy shape, the SD9 looks as if it was styled by committee in a 20-minute meeting. It's not outright ugly--just bland and occasionally old-fashioned. Constructed of a metal chassis and a polycarbonate shell, the camera weighs two pounds without a lens but with batteries and media installed. That's only a bit heavier than other entry-level digital SLRs.

With only a few exceptions, Sigma placed the controls intelligently. The exceptions? The shutter-speed dial, a rotating knob on the camera's top cover, comes straight out of a 1970s design manual and is hard to reach without taking your finger off the shutter release. And we found the skimpy viewfinder information display irritating; it doesn't show metering mode, white-balance setting, or shots remaining. Furthermore, though the menu system is easy to understand and navigate, you shouldn't have to use it to change the white-balance setting on a professional camera. That should be accessible via a dedicated button.

Not your typical exposure-mode control dial.

LCD and menu navigation are pretty typical for a digital SLR.

Sigma endows the SD9 with a slightly below-par feature set for its class. On one hand, the exposure, white-balance, and metering system is fairly comprehensive and includes all four standard exposure modes, seven white-balance presets, manual white balance (but no color-temperature adjustment), and three light-metering modes. There's no on-camera flash, but that's fairly common for a digital SLR. The camera's hotshoe will accept powerful external flashes, including Sigma's EF-500 DG Super SA, a TTL-dedicated strobe with a guide number of 165 (at ISO 100).

The SD9 shoots only Raw files, so get used to looking at this interface.

You can attach the camera to your PC via USB or FireWire.

Only Sigma's SA-mount lenses are compatible with the SD9, but that's hardly a limitation; Sigma makes 41 SA-mount lenses in focal lengths ranging from 8mm to 800mm. The size of the Foveon X3 sensor results in the camera having a 1.7X multiplier--multiply 1.7 times the focal length of the lens to obtain its equivalent on a 35mm camera. Plus, the SD9 has a unique, transparent protective cover just inside the lens mount to keep dust off the sensor. Dust on the CCD is a recurring and irritating problem on other digital SLRs.

But the SD9 captures images in only Raw format, so you're out of luck for quick-and-dirty test shots that you can share immediately with a client. The included Sigma Photo Pro software, developed by Foveon, is nonetheless a powerful Raw file-processing application. It makes reasonably quick and easy work of fine-tuning exposure, contrast, color balance, and color saturation.

The camera's most serious limitation--and it's a biggie--is its limited light sensitivity. Not only is it restricted to settings of ISO 100, 200, and 400, but the ISO 400 images show severe noise. This makes the SD9 far less versatile than competitive digital SLRs, most of which can shoot acceptable photos at ISO 1,000 or higher. And, inconveniently, the SD9 uses two separate battery systems.

Two--count 'em, two--sets of batteries power this camera.

Like its design, the SD9's overall performance is adequate but lags a step or two behind the competition's. Shutter delay and shot-to-shot times are roughly average for digital SLRs. In continuous-shooting mode, the camera captures a lackluster 1.9 frames per second (fps) for a six-shot burst. But once the buffer is full, those big Raw files really bog down, forcing 10- to 15-second delays between bursts.

In addition, the SD9's autofocus system lags at least a generation behind those of other digital SLRs. We missed several shots, in good light and bad, while waiting for the AF to lock or track moving subjects that it should have been able to handle more easily.

The camera's so-called sports-finder viewfinder shows a view that's roughly 25 percent wider than what the camera captures. The area that won't be recorded is clearly distinguished by a transparent gray mask. We like the ability to see what's just outside the frame area, but the actual image area is fairly small in the viewfinder, which makes manual focusing more difficult. The camera's LCD is sharp and reasonably easy to use in bright light for playing back images.

We never exhausted the pair of disposable lithium CR123A batteries that run the camera's mechanical operations, which should have the same life as they would in a film camera. And we got many hours of use from the two disposable CR-V3 batteries that power the digital side. You can also use AA batteries, either alkaline (if you're brave) or nickel-metal-hydride, for the digital functions.

When the camera is set at ISO 400, images get significantly noisy.

The real differentiator for the SD9 is its use of the Foveon X3 CMOS sensor. Each pixel location on the X3 contains three vertically stacked photodetectors, which are optimized to capture red, green, or blue light. In contrast, all competing imagers use one layer of sensors overlaid by a pattern of alternating red, green, and blue filters; the sensor captures only a single red, green, or blue primary at each pixel location and algorithmically builds a complete image in the camera by interpolating the two missing color values for each pixel from the data gathered by adjacent pixels. (See the Foveon Web site for more on this.) Foveon claims that its X3 sensors provide much sharper pictures than conventional sensors, with better color detail and fewer color artifacts such as moiré.

Under only moderately bright lights, colors come out fairly desaturated.

True, the SD9 is capable of capturing some exceptionally sharp images. With well-lit subjects that contain very fine detail--woven fabrics and highly detailed landscape or architecture shots, for instance--the SD9's images often amazed us. They appeared significantly sharper than any we've seen from conventional sensors with twice the pixel resolution. Also consistent with Foveon's claims, the X3 sensor resists color artifacting, especially the kinds of moiré that can plague shots of clothing and hair.

The SD9 picked up the weave of the fabric (left), which totally escaped the Nikon D100 (right).

However, the images didn't stack up quite as well on other fronts. Their colors tend to appear a bit undersaturated. You can easily correct that with the Sigma Photo Pro software, especially if the subject was well lit. Still, we had persistent trouble getting juicy yellows, oranges, and browns.

In addition, our test images showed much more noise than competing SLRs produce, especially in shadows. Though this often looked much worse on screen than in print, it occasionally affected the smoothness of solid-colored objects. Red hues show especially high levels of noise and frequently emerged in prints as muddy, impure color. The noise problem becomes even more severe at higher ISO settings. Shots taken at ISO 400 showed nasty, multicolored noise that would ruin many prints.