Tamron SP 150-600mm F/5-6.3 Di VC USD lab test report

The Canon 400/5.6 is I think better and in the ballpark price-wise.

http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=929&Camera=453&Sample=0&FLI=3&API=2&LensComp=278&CameraComp=453&SampleComp=0&FLIComp=0&APIComp=0

The Canon is also better 560mm vs. 600mm if you add an extender. It doesn’t zoom so quickly though (what with all the adding and removing of extenders).

BTW the 100-400 is an antique and a maybe to get replaced real soon (Canon have patented a newer version, so there’s a reasonable chance). The Canon 400/5.6 also has no IS, but for wildlife you need the shutter speed anyway.

Oh and no, I don’t have either of those lenses, I get to 400+ with a 300/2.8 IS and extenders (or 70-200 II with 2x extender, etc.). Neither of which is close enough in price to mention any more (the 100-300 on m43 is, as it is a 2x crop, but it’s more okay than great).

Source Article from http://www.dpreview.com/news/2014/06/25/tamron-sp-150-600mm-f-5-6-3-di-vc-usd-lab-test-report