You could be forgiven for thinking that Japan's Sigma is just a maker of lenses for the cameras of other companies like Canon and Nikon, but that's not the case. The company broke into the digital camera market in 2002 with the SD9, which was also the first outing for a new sensor technology developed by Foveon. Unlike other sensors that capture one color per pixel location, the Foveon X3's stacked design captures all three colors at each pixel, which is said to result in more accurate color reproduction and sharper resolution. Now Sigma is about to release a new camera sporting a new version of the X3 sensor, dual image processing engines and improved ISO sensitivity. It's also very expensive...

After announcing the medium format SD1 at last year's Photokina, Sigma will release its new flagship digital SLR camera to the professional and pro-sumer market early next month. The highlight of the new camera is of course the 15.3 x 3 megapixel Foveon 23.5 x 15.7mm APS-C X3 direct image sensor. Sigma says that Foveon's engineers have managed to enlarge the CMOS sensor while narrowing the pixel pitch to more than triple the 14 megapixel resolution used on other Sigma cameras to 46 megapixels (4,800 x 3,200 x 3), although bumping up the actual 15.3 megapixel quality up to the full resolution will require some software intervention.

The color filter array sensors common in other cameras can only receive either red, green or blue light at each location and complex algorithms are needed to estimate the values of absent colors at each position before a full image can be formed. The new X3 system comprises three silicon-embedded layers of vertically stacked photodiodes designed to absorb all red, green and blue color information at each and every pixel location for film-like color and sharper resolution.

The lack of color filters also means that the output doesn't suffer from false color patterns to which such systems are prone and so dispenses with the need for a low-pass filter in front of the sensor.

Faster processing, better quality

The camera's 11-point shifted twin cross type sensor promises improved autofocus accuracy and coordinates with a new 77-segment AE sensor for better exposure in challenging lighting conditions. There are four metering modes to help with exposure control.

The SD1 receives a two stop sensitivity increase over the SD15 with a range of ISO100 to ISO6400 and benefits from improved image processing and noise reduction algorithms. Interference from vibration is also kept down by the use of a two-motor system for mirror drive and shutter charge.

The new model includes two TRUE II image processing engines that are said to provide richly toned, high resolution images and improved processing speed. There's also simultaneous capture of RAW and JPEG images - a first for Sigma cameras - and the option to select full-size, half-size or quarter-size RAW files. To better cope with higher volumes of color data, the SD1 makes use of DDR3 buffer memory, with continuous shooting of 5 frames per second and capture of up seven RAW images in one sequence.

Sigma's decision to include its SA bayonet mount gives it compatibility with over 40 of its own lenses. Despite Sigma's Mark Amir-Hamzeh announcing that this will give SD1 users a huge advantage, owners of Canon or Nikon lenses will still have to head for adapters before being able to shoot through a favored lens.

Tough, weatherproof chassis

The chassis has a similar feel to classic 35mm SLR cameras, is protected from the odd bump by a magnesium alloy body and has its O-ring connections sealed against dust and moisture. The pentaprism viewfinder has 98 percent horizontal and vertical coverage and diopter adjustment, and the 3-inch, 460,000 pixel resolution LCD monitor enjoys a wide viewing angle.

Sigma says that significant improvements have been made to the user interface for a faster and more convenient experience. Highlights include the placing of exposure mode and compensation buttons on top of the camera for easier access, the aperture and shutter speed can now be set using dedicated dials and commonly-used functions have been brought together in Quick Set menu options.

Images are recorded to a UDMA mode 6 compatible, TYPE I Compact Flash Card in 3:2 aspect and can be manipulated using the bundled with Sigma's Photo Pro 5.0 processing software. Unlike many competitors in the current digital SLR marketplace, the SD1 doesn't shoot video.

Weighing 24.7 ounces (700g) minus the Li-ion battery and card and having dimensions of 5.7 x 4.4 x 3.1-inch (145.5 x 113.5 x 80.0 mm), the SD1 carries a suggested retail of US$9,700. This puts its pricing way out in front of Canon's 1D and Nikon D3S, and more in line with the Pentax 645D, which has a much larger sensor (44 x 33mm).

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