gruhl28 said:
I read all the time about one lens rendering better than another, people preferring the "look" from one lens, one lens looking flat whereas another looks 3D, etc. I wish for once someone would post comparisons of THE SAME SHOT taken with two of these lenses so those of us who can't purchase all of these lenses would be able to see for ourselves whether there really is a difference visible to us. I've seen people post photos from different lenses supposedly showing a difference, but they're always completely different scenes, with different lighting.
I understand your request very well. I have tried to find good comparison pictures as well, without much luck.
My most relevant experience was a night I had some friends over playing a game. I took pictures with both the Sigma and the Canon 50L that night. Same camera, same light source and angles, same apertures (f2-f2.8), same people. The day after I selected the pictures I liked, and ended up with 3 from the Sigma, and close to 20 from the 50L - and I had about as many pictures with each lens to begin with. The main difference was that the Sigma-pictures looked flat and lifeless, and the Canon 50L-pictures had much more depth and "life" to them.
I have deleted the pictures I didn´t like, and I don´t want to share pictures I have left of my friends online. Besides the few Sigma-pictures I kept was pretty good and wouldn't illustrate the difference very well.
I would also like to mention that my wife, who has no technical interest in cameras or lenses, also preferred the Canon 50L pictures without hesitation. (And she didnt know which lens was used...)
That is why I encourage you to have a look at different flickr-groups where the Sigma 50 Art and the Canon 50 L are used. When you look at the 50L-groups, be aware that you find way to many pictures taken at f1.2, and/or which is slightly out of focus. I think the strength of the 50L is between f2 and f4, and you will have to look for those pictures as if you were looking for a needle in a haystack.
I think the pictures "Johnny [shakedown]" takes generally are very good at illustrating how well depth is rendered by Canon L - primes: https://www.flickr.com/photos/johnnyshakedown