In 2005, Canon released what was heralded as the first "affordable" (for non professionals) full-frame 35mm digital SLR, the Canon EOS 5D. This in itself was enough buzz to sell a higher resolution, more expensive, mid-range camera than the EOS 20D. The subsequent Mark II model, released in 2008, was an update to match changing market conditions in those three years, including a focus on video capabilities (to the frustration of some, the joy of others). In 2012, the Mark III joins the Mark II.
The top of the Canon EOS line-up is now unambiguously the EOS-1D X; followed by the EOS 5D Mark III, EOS 7D, and 5D Mark II. The 5D Mark III feels like it is a mix of the other three cameras. It has upgraded the single Digic4 processor of the 5D Mark II to one of the EOS-1D X Digic5. It has borrowed the 61-point AF system of the of the EOS-1D X, but with only a single Digic5 processor operates noticeably slower and lacks the advanced subject tracking mode. For many studio and portrait photographers, the EOS 5D line has been sufficient: it provides excellent resolution and full frame depth-of-field. The EOS 5D Mark III, with in-camera lens correction, dual car slots, and Canon's leading resolution sensor is an excellent studio camera for less than the flagship EOS-1D X.