Sigma's DP range has had more incarnations than Batman, with the Adam West original DP1 long relegated to history by the current daring duo of the DP1x and DP2x. The DP1x marked the debut of Sigma's "Analog Front End" (AFE) technology in the DP range, originally announced as part of the SD15's specification; more significantly it marked the unification of the DP2 and DP1 body design and layout; the DP1x improvements have made it back to the DP2x now and it seems that this is the point where the DSLR (SD15) and compacts (DP1x, DP2x) should in theory deliver identical results bar optics. All are based on TRUE II, AFE, Foveon sensor.

The original DP1 was marketable on the strength of the 16.6mm F4 lens - which gave a nice, wide and sharp result. Having not messed with the optical formula, the performance improvmenets are all on top of the original DP1. Let's look at what the current state of the art is for Sigma's groundbreaking compact...

The DP1x is the first major upgrade of the DP1 - the interim DP1s did not meet the expectations of many pundits and retained the TRUE processor and button layout of the original DP1, whilst adding a few refinements for faster AF performance. As such, the DP1x represents the model most DPx enthusiasts have been waiting for - with the Analog Front End update an bonus that then leads to the creation of the DP2x. At the time of writing, the DP1s has dropped out of circulation entirely and the DP1x is typically offered for the retail price - now £619 thanks to the VAT increase, whilst the technically similar SD15 DSLR is £849 and the DP2s (the DP2x is announced, but not yet on sale) is available slightly discounted at £479. The original DP1 still shows on some suppliers' lists at £299.

As with the original DP1, the DP1x sports a 16.6mm F4 lens which has met with positive reviews, and it inherits functions from the DP2 like the live histogram display, QS button and dedicated "setup" position on the control wheel. Manual override remains easy, with up/down control for priority modes (doubles as zoom control when in playback; the digital zoom function of the DP1 has long been abandoned) and shutter speed for full manual whilst left-right on the four-way controller adjusts aperture. As a pioneering digital compact camera, the DP1's properly adjustable aperture was a bit unusual - now the genre is picking up competitors it's still a plus point when comparing it against higher-end small sensor compacts.

The DP design has been available for three years now - the original DP1 going on sale in April 2008 - and has seen few revisions since the April 2009 release of the DP2. The s and x models have been refreshes rather than significant updates (economies of scale suggested that the DP1 and 2 should share rear panels and pipeline the moment the DP2 was announced!) yet the system does remain unchallenged at the price point. There may be other things you could spend £600 on, but you cannot as yet buy a large sensor digital compact for so little; the rival systems are the Leica X1, at £1400, and Fuji's recently announced X100. Whilst not directly comparable, the compact Micro Four-Thirds systems offer interchangeable lenses for roughly the same price - body only - and the Sony NEX series is perhaps the strongest challenge to the "serious compact camera" positioning.

The sensor remains a 4.5Mp x 3 Foveon unit, a revision of the sensor first seen in the SD14 - with microlenses to optimise the relationship between lens and pixels and minimise falloff, no AA filter and an integrated non-removeable IR filter. It can be removed, but not by design and not easily, unlike the SD range. AF is contrast detect and much improved over the original DP1, though firmware updates to the earlier cameras close that gap. Storage is by SDHC card and the battery hasn't changed either; finally the display - improved over the first models through firmware - is the same 230,000 pixel 2.5" unit from the 2006 announcement.

Live view performance of the DP1x is much improved, with better colour and contrast, and the DP2-style button layout is more intuitive and provides a larger grip surface on the back. Improved silk-screen logos help make the controls more obvious.

The real reason to buy a DP1 has always been the combination of the 16.6mm F4 lens and Foveon sharpness in the compact body; nowhere does this become more apparent than when you put it up against the SD15 and 17-70. Trying to match the two cameras as much as possible, the 17-70 comes off rather badly with OS off (after all there's no OS in the DP1x), whilst the DP1's showing is marred by the flare resulting from the lack of a standard lens hood it's still apparent on the full-size version that the corner sharpness - even fully open - remains as good as the original whilst the changes to the image pipeline suggest that the DP1's lens gives a warmer rendition or the DP1's idea of "Neutral" mode is slightly different. Unless the two cameras aren't as evenly matched as they should be, of course. Proper colour testing will be done later.

The Sigma SD15 WB Auto, Colour Mode Neutral 17-70 OS off, F4, 1/320th	The Sigma DP1x WB Auto, Colour Mode Neutral 16.6mm F4, 1/320th