COLOGNE, Germany--Sigma announced its SD1 SLR at the Photokina trade show here yesterday, and here's how it looks in person. The magnesium-alloy chassis, which the company itself said it makes, comes with a deep handgrip for the right hand. This version is shown with a Sigma 18-200mm zoom lens. Sigma's earlier SLRs haven't fared well in the marketplace, but the company hopes the SD1 will fare better in part through a larger and improved Foveon image sensor. The new model, measuring 24x16mm, has a 15.3-megapixel resolution, but unlike the vast majority of cameras, each pixel captures red, green, and blue light, not just one of those three.