Originally Posted by Chewy734
So... Basically you want an APS-C sized sensor in a 5D3 or 1D X body.
No, it's about pixel density and telephoto "reach". The number of pixels on the subject in a focal length limited shooting situation, like birds, is determined by the focal length of the lens and the pixel-density of the sensor. The problem is controlling noise as pixel-pitch gets lower.
I'd just as soon have a full-frame sensor, but with the pixel-density of the current 7D, but with improved SN ratio, better AF system and AF to f/8.
If I spend $13,000 on a 600mm lens, then I want to be able to use it with a 2X or 1.4X TC so that I've got 600mm, 840mm and 1200mm at my disposal with AF. I'd rather have a compact body, like the 7D or 5D.
The 1D-X was not designed for optimal performance in focal length limited situtations. It's still a fine bird/wildlife body, particularly in very low light, but it's really not aimed at the market, like the 1D MkIV was or the good, but flawed, 7D. (Unreliable AF and relatively poor high-ISO performance). The 1D-X excells when used with the right focal length lens for the situation, so giving it f/8 AF is HUGE at increasing its versatility. I may end up owning one, but I'm waiting to see how both my 5D MkIII and the 7D MkII works out. If they get f/8 AF, then I'll be sticking with them.