Despite its position as one of the lowest-cost digital SLRs on the market, the Sigma SD10 has some of the most innovative technology. Together with its SD9 predecessor, released in 2002 but still available, these are the only reasonably high-resolution users of the Foveon X3 sensor – although Polaroid offers a 2mp version on a consumer camera.
The X3 is a form of CMOS sensor with its colour-sensitive elements arranged in layers, which is equivalent to the way that colour film works. Three diodes are buried at different depths in each cell. Red, green, and blue light penetrates to different depths, so the camera can work out the mix of colour for each cell.
Conventional CCS and CMOS sensors arrange different coloured filters side-by-side over adjacent cells, each of which see a different colour. The camera interpolates between different cells to achieve full colour for each pixel, but there’s an inevitable slight blurring of fine detail.
The X3 doesn’t need to interpolate between cells, so the detail is extremely sharp. Consequently the 3.4mp Sigma SD9 and SD10 produce images that are at least as good as their 6mp competitors, and sometimes better.
Sigma is best known for the high-quality lenses it makes to fit most other cameras, and it makes film cameras too – the SD9 and SD10 are based on the SA 9 35 mm SLR. It’s a perfectly respectable design with all the controls you’d want, matrix and spot metering, plus a motion-predicting autofocus. However, these cameras use Sigma’s unique SA lens mount, which isn’t supported by other makers. You’re confined to buying Sigma lenses, but there’s a decent choice across a wide price range.
The film camera basis of the SD10 is obvious in its viewfinder, which shows a much wider area than the sensor can actually capture – the non-capture area is greyed out, which is useful as you can see moving objects just before they enter the frame. Sigma calls this a sports finder, but the real reason is that the 35mm film area is bigger than the X3 sensor. The SD10 only sees the central area of each lens’s projected image, giving an equivalent magnification of 1.7x. Consequently, the 15-30mm lens tested gave a similar image to a 25-51mm lens on a film camera, and the 70-200mm lens was the same as a 120-340mm lens.
The main difference between the SD9 and SD10 lies in the configuration of the X3 sensor. On the SD10 it’s overlaid by a grid of convex microlenses, one for each cell, which increases the light-gathering power but carries a slightly increased risk of halos.
As a result, the SD10 now has two ISO sensitivity modes. In Default mode you can select from ISO 100 to 800 and take long exposures up to 15 seconds at ISO 100, or four seconds at higher sensitivities. Extended mode lets you select from ISO 100 to 1,600 (which is fairly noisy), with long exposures of up to 30 seconds at any sensitivity. There seems little reason not to leave it in Extended mode all the time.
The SD10 camera body is almost the same as the SD9. It’s relatively large and obviously plastic. However the underlying chassis is metal, and a plastic outer body is tough enough provided you don’t use it to hammer in nails. Immediately behind the lens mount is a glass filter to protect the sensor from dust.
The 1.8-inch LCD monitor on the back can now optionally display a three-colour exposure histogram plus full exposure details on playback. Accidentally deleted images can now be recovered provided you don’t overwrite them.
The battery tray takes four AA rechargeable batteries, or two long life lithiums, but the SD9’s second battery compartment has gone, making the handgrip less prominent. Battery life isn’t as good as the SD9, but you can run the camera from a supplied mains adaptor.
The only notable omission is a pop-up flashgun. Many photographers prefer to use a separate flashgun, but it’s handy to have a built-in unit for emergencies, or fill-in lighting of shadows.
The SD10 takes a CompactFlash II memory card or Microdrive. Unusually in this price bracket, there’s a FireWire port as well as USB for downloads.
SD9 and SD10 will only save in the unique X3F Raw image format, with lossless compression – unusually there’s no compressed JPEG option. X3 file sizes vary – most are about 5MB but can be anywhere between 4.4MB and 9MB.
Sigma’s own PhotoPro software can open the X3 files and convert them to standard formats such as TIFF or JPEG. PhotoPro is fortunately very good, with a wide range of image enhancements that let you fine-tune exposure and colour balance problems before exporting the pics. A new X3 Fill Light slider control is particularly useful for brightening shadow and mid-tones without the image looking unnaturally flat. You can do an awful lot to turn marginal images into winners at this stage.
Image quality from this budget digital SLR is excellent. The images are as good as most 6mp digital SLR samples we have, though the best of the latest 8mp prosumer models do start to show finer image detail. It’s a close-run thing though. If you need an interchangeable lens digital camera and don’t mind committing to Sigma’s unique SA lens range, the SD10 is a fine choice.