Here it is - the DSLR every Sigma enthusiast has been waiting for since the first announcements. Externally a very similar camera to the SD14, the SD15 represents a major overhaul of Sigma's digital SLR system and even at first glance, can be seen to be a substantial upgrade in many ways. This review is a quick introduction to the hardware and some of the more obvious new features of the system, and should answer many of the questions Sigma users have been asking whilst addressing some of the requests from the SD14.

Sigma's SD15 is the culmination of development around the TRUE-II processor first seen in the DP2 and the TRUE architecture launched with the DP1 - the previous SD14 model used custom DSPs, whereas the DP range and SD15 see a standardised image pipeline across Sigma's range of Foveon cameras. This has allowed the SD15 to mature in it's own right and move significantly forward from the previous camera.

A UK RRP of £899 sees the SD15 competing in the "pro-Amateur" level of the market and is a much lower price point than previous SD models at launch (the SD14 was £1199); it's also the highest-performing Foveon DSLR yet with a 21-frame continuous shooting buffer and a new dual-motor mirror mechanism allowing for full mirror lockup operation. The shutter is even quieter than the SD14, making the SD15 the ideal discrete camera for social photography, weddings and events.

Further improvements over the SD14 include a larger 3.0, 450,000 pixel LCD (larger than the DP-series), ISO 3200 mode and a new 77-segment metering syste which gives more consistent exposure whilst using the high dynamic range of the Foveon sensor to deliver the best results.

Detail revisions to the SD15 include a backlit top LCD (with a new layout), improvements to the AFE - analogue front end - of the Foveon image pipeline and a move to SDHC card storage. Whilst many users feel that Compact Flash is the more mature standard, SD cards are a smaller physical size, cheaper to buy generally and offer excellent transfer rates with the highest-end cards. More importantly an SD15 user does not need to use multiple types of card with their DP models and many laptops and computers (such as Apple's iMac/Macbook models and most netbooks) include SD-card readers as standard.

The reality of the SD15 is that it's a huge improvement over the SD14 in speed and usability. The buffer allows for seamless shooting where previously the SD14's limited capacity for raw files could slow users down (though at the time of launch, most cameras moving 14Mp of data had a similar capacity buffer - they just chose to publicise their smallest JPEG figures). The AF is faster and works better in low light, and the 800 ISO image quality is distinctly better, offering a useful expansion to the capabilities of the SD model.

Where the most progress has been made is in the user interface however. The larger screen has been used to deliver improvements like the function menu displayed to the right here, with rapid access to ISO, flash modes, metering and shooting information in a way never before seen on a Sigma DSLR. The large, clear display also allows the image preview to carry more information, and an innovative histogram-aware zoom function allows exposure of a given area to be quickly checked.

Due to the demand for the SD15 we've only had a limited time to put this review together, so this will be updated when we have more time to use the camera in different situations. In the meantime see the next page for more pictures of the camera itself.