ravnish said:
i dont understand why we cant have just a simple digital 50mm f2 compact
The problem is lens design restrictions:
Compact cameras tend to have the lens quite close to the film plane, this leads to the light hitting the film at quite a steep angle, and digital sensors don't like it at all (Foveon, with its three layers even less than a bayer sensor), essentially trying to put together a package with a 50mm (equiv) f2 lens that properly covers an APS sized sensor will probably lead to a digital "compact" almos as big as a DSLR.
Even with film, when designers decided that small size was paramount, fast lenses have never been an option and f3.5 or f2.8 at most were used.
The Foveon sensor, despite not being too good in low light, still has a good 2 stops advantage compared to the average tony sensor used in digital compacts, so at f4 you still have an half-decent low light performer, but with good lighting you should get pictures as good as the ones produced by an 8-10 MPix DSLR.
About the 28mm equiv, Sigma seems to think that the sensor is so good that you can use a significant amount of cropping and still get good decent sized print, while if you have a longer lens, you can't widen the angle of view later.
A quick calculation shows that you can crop the 28mm fov to a 35mm fov and still get an image with more pixels that the SD9/SD10 so still in the DSLR quality range, cropping to 50mm equiv may probably mean pushing it a bit too far, and being unable to get good prints past 7x5, still better than nothing.
