So, here are a few shots with the Sigma 300mm F/2.8 lens with the Pentax K-3. And with the Canon 1D mark IV, 7D & Canon 300mm II lens.
I did not post process any of these. But, I did brighten them up some.
Oddly enough the Pentax K-3 and Sigma, by F/3.5-4.0 is right there with it. That is about what I thought was going on before the test. The Sigma lens at F/3.2-F/4 sharpens up nicely. The Mark IV is pretty much out of the running at this distance.
The 1D mark IV and 300mm lens is pretty much out of the hunt. The K-3 and the 7D rake it over the coals at this distance.
The new Sony sensor can shoot at 1250-1600 ISO with no problem. With outstanding DR. Making it a better sensor than my 1D mark IV. And with 1.5 crop factor to boot. 1D is better at BIF. The only reason I use it at this point.
These are the average distances I shoot birds at. 20-30 feet. So a good test for me.
IMO, there is a reason Nikon and Canon do not put out a high end crop sensor camera. It would kill there FF sales in the wildlife arena. It won't be long before they have to address it. Or they will start loosing customers IMO.
Next I will shoot the Canon 500 II and the Sigma 500 4.5 to see the difference.
Cheers and good birding.