There are many, many comments in the the threads about the 7D having a 1.6x longer reach for bird and nature photography than the FF. Those of us who have both FF and 7Ds (Neuro et al) reckon that in practice the difference in reach isn't much in practice and the higher IQ of the 5DIII or 1Dx etc gives overall better images. This morning, I decided to have a shoot out with the 300mm f/2.8 II + 2xTC III on a 7D vs a 5DIII. Both cameras were hand held, but resting on the shelf of a hide (blind) at sufficiently high shutter speeds that there was no camera shake. Iso was at 640 and the aperture at f/5.6. I post 6 collage pairs out of many shots, which were are representative. The 7D images are at 100% crop (the actual number of pixels). The 5DIII have the number of pixels increased by 1.5x in each of width and height. All images were taken in RAW, and the sharpness and luminance set at 25 units in PS. The crops were cut and pasted into PS jpegs, and the collages sharpened using USM at 0.5 radius and 100%.
The results parallel what I have found many times in the past.
In terms of resolution
1. At very far distances where the cropped image on the 5DIII is about 200-400 pixels high or wide, the 7D is marginally better.
2. For larger images of say ~500-800 pixels high or wide on the 5DIII, it is at least as good as the 7D, if not better.
3. For images greater than a 1000 pixels, the 5DIII is very clearly superior.
The noise is better on the 5DIII.
Dear Sir , Mr. AlanF.
Thousand Thanks for you Testing and Spend a lot of your time to Show and Teach us.
Just One more thing that I would like you to do for us again---Use That two Beautiful systems and Shoot the Doll or the Colorful Jar or Bottle of Wine ( The Doll or the Bottle of Wine can not Move), And The Cameras On the Tripods( With Remote Control or Self Timer) = That will show the real Sharp of the same photos with out motion blue of the real Birds.( Yes, Sir, I Know that your Strong Hands and do not create the Motion Blur when your press the shutter)
Again, Thanks you, Sir.