Interesting way you have of inverting the colour resolution issue Smiley Foveon sensors have stable resolution across all colours, Bayer CFA sensors have variable resolution across colours. You can see this quite clearly in Mike Chaney's (ddiSoft, makers of Qimage) comparison with his 5D using colour resolution charts. It is the 5D that struggles to match the SD14 resolution. Admittedly this is a worse case, using the kind of highly saturated near primary colours of the flowers he uses but it makes the point, even if it is rare to hit that exact situation. Ah. You beat me to it.
Sigma's marketing idiocy aside, the sensor has a true 14 million pixels. This is like on your monitor - a pixel is a full-color range location. Same as film if you are scanning it. The problem is compounded by the fact that Bayer pattern sensors, which are
sub-pixels are being marketed as the real thing. So we end up with marketing claims that are as clear as mud for the most part.
The only real advantage of the Sigma is that the color channels have identical resolution. This produces very good and realistic colors and a very film-like shoulder as well. There also are no real issues with moire from the color, since there is no real "pattern" for the camera or software to interpolate. So it takes very very good scenery shots.
But it has a fatal flaw in it, like film, because it works like film does. It shoots at one ISO only. Anything other than the base ISO is a bunch of computer trickery. So it is pathetic if you push it more than a stop or two, just like film. Given that the "base" ISO seems to be about 50-100 on it, it's exactly like throwing some Velvia in your camera and trying to use it for absolutely everything. Slow shots will look stunning. Action and low light... yeah... not going to happen.
So it's really the world's best scenery DSLR camera. And for that, if it were priced at a reasonable $2000 or so, it would be a tremendous tool for people who do that sort of thing. (such as myself) But at that price? Not going to touch it.
Me? I'm a bigger fan lately of the Fuji sensors. They are inexpensive and their pixel binning and diagonal pattern combined with their HDR mode that brackets and blends inside the camera essentially gives you the cost advantages of a cheap Bayer sensor but pretty much none of the problems. (especially of note is the way it doesn't completely wash out over-exposed areas) The pictures it takes are *this* close to the Sigma. But the price, well, Fuji's putting that top-end EXR sensor in under $500 cameras.
Given Sigma's so-so glass, the sad thing is that the Fuji HS20EXR has a similar cropped sensor but a very nice lens - and will probably work 80-90% as well as the Sigma SD1 in terms of output and 200% better in terms of action and low light shots. Even without interchangeable lenses. For $500.
Verdict: Love the Sigma. Will buy the Fuji instead. Doubly so if Fuji ever releases a DSLR version of that thing.
EDIT - before everybody jumps all over me, let's do a little "napkin" math:
- The Sigma sensor is being calculated to come in at about 30MP equivalent. Or about 25% better than a 24MP DSLR.
- If you calculate out the geometry and interpolation losses in a Bayer sensor, and then factor in the AA filter, you end up with roughly a 0.65-0.7x multiplier for most DSLRs in each dimension. This gives you a rough idea of how many actual full-color locations you can expect. This allows for easier comparison between technology types.
- The Sony 24MP DSLR comes in at about 11 million actual pixels. The Sigma has 14 million. Or about the same 25% difference.
- The Fuji at 16MP has a closer to 0.8X multiplier (give or take) and comes in at about 11MP as well. (scanned 35mm film is closer to 3-4MP, btw)
- The Sigma has a bit over 14MP and a 1.0x multiplier.
What this means is that the cameras are all about the same other than that 25% bigger picture/resolution for the Sigma. But I think Sigma's glass is 25% *worse* than the competition, making it a wash versus the three technologies. Ouch. (actually the math hurts Sigma more, as worse glass has a myriad of other issues with it in terms of image quality aside from absolute resolution)
$500 bridge camera does almost exactly as well as Sigma's new toy. Man, that's got to hurt...