[Update: There is a second test in the comments section in this article]
Alright, let me put it like this, today I was going to test how the Canon 100-400 4,5-5,6 IS compared to Sigma 50-500 4,5-6,3 OS and I was a bit afraid of testing these two cameras against each other because the 5D has 21MP and I got 4.6MP. There’s a slight difference. :)
First image has been shot using ISO200 on both cameras, Sigma at F7,1 and Canon at F6,3 .
I used Lightroom 3 beta 2 for Canon and Sigma Photo Pro 4 for the Sigma.

Original Canon 100-400 IS has a VERY sweet bokeh! Yummy! (right shot)

Original (here I pushed sharpening on the Canon version, and some to the Sigma shot as well. +0.3) You can see how much more detail the Canon has – but my Sigma is not too afraid of the fight.. :) Looking at this shot I get the feeling that Canon’s 100-400 has the edge in terms of sharpness but that said, it’s not easy to see without those extra pixels. mmm
Second shot: Sigma at ISo50, Canon at ISO100. I tried to make WB as similar as I could. Wasn’t that easy. Canons bigger sensor gives a nice blur to the background.

Original I took quite a few shots and none of them from the Canon came out very sharp. I’ll redo this another day. Or is this how it’s supposed to be?

Original Difference here is quite small. In order to take the Sigma shot, I walked away 5-8m to make background blur more. Didn’t help much.
So, don’t make hasty conclusions about this test. Having better optics on both in controlled situations the 5D would probably win by a wider margin. I think.
Part 2 (before in the comment section but due to problems with WordPress I put it here so that you can see these pictures)
Next test! Now I switched lens to 120-300, left Sigma, right Canon. Sigma shot at f5,6 @ 120mm. Canon 100-400 IS shot at F9 @ 100mm. I will have to do a third test. :) And I found Canon 24-70 2.8L lens isn’t sharp enough for these tests.. I wonder if the 24mm TS is better? Anyhow, the 100-400 lens from Canon looks very good, all the way from 100-400mm – it degrades slightly at 400mm but the Sigma 50-500 degrades much more, especially at corners. Will come back to this.







This one shows how sharp the 50mm 1.4 Sigma is. I tried to use it for above comparison against 24-70mm 2.8 L but failed to frame it correctly.



