Jim, I think a large part of the difference is that the Sigma image is correctly exposed, but the Canon is underexposed. You had ISO 400 and 1/1000s for the Canon.For Sigma, you set ISO 200 and appropriately doubled the time to 1/500s. However, you also increased the aperture from f11 to f9. This is a good 2/3 stop, so if the f9 exposure is correct,the f11 would be sufficiently underexposed to look darker and have less vibrant colours.I am assuming you used manual settings. If auto, then either the light went off the foreground for the Canon pic, or the Canon is not auto-exposing accurately.
A comment regarding the colour, as you mentioned in the Forum Jim. As you said, the Sigma wins out every time. I found (which is why I opted for Sigma years ago) the conversion to B+W is excellent - predominantly because of the colour response in the first place.
