Although this is not a thorough review, I would like to give everyone a fair opinion of my experience between the two cameras. I had the chance to go up to Canon Headquarters in TST this afternoon and out of curiosity I decided to play with the 5D Mark III once again.
Now what I am concerned with isn't the fancy HDR, or Rate It functions (useless), but rather the AF response and speed of the actual camera. Of course as some of you guys may know, I have recently purchased a 1D Mark IV. I decided to go with the 1D Mark IV over the 5D Mark III for several reasons.
1) Speed of the Camera (10/FPS)
2) Overall Built Quality and Feel of the Camera
3) Shutter Life (300k vs. 150K)
4) Uncertainty of the new 5D3 AF system
5) Better weather sealing than the 5D3 system
6) I wanted to go crop sensor because I was kind of sick and tired of the vignetting with wide lens at FF
7) PRICE, at $34900HKD, the 1D4 is a steal, where as the 5D3 at $27400HKD is a bit overpriced (especially if you think about the fact that you will need to buy a brand new grip with it at around 2500HKD).
8) No Optional Grip Vs. Optional Grip. The 5D2 grip was a pain in the ass. Always had a problem with the grip loosening itself and thus loosing power to the camera and it never really felt right where the 1D4 had a built in battery grip, and the grip felt much better than the 5D2 grip (maybe this will improve with the 5D3, we'll have to wait and see.
Well after trying the AF of the 5D Mark III for over 30 minutes, I do find it to be slightly faster than the AF on the 1D Mark IV. Mind you though, I was comparing it with the 1D Mark IV at the canon showroom which is about 2 years old with a poorly conditioned battery (Battery power has a lot to do with AF speeds and also shutter speeds), while the 5D3 is obviously a installed with a brand new battery less than a week old.
SO WHICH IS THE BETTER CAMERA?
I would still say 1D Mark IV for stills photographer. WHY?
Well mainly because the 1D was also meant for serious stills photographers of all kinds but since the last 5D (5D2), 5D is now more a videographer or indie filmmakers' camera. So it's hard to say which is better. Rather the question should be which is more suitable for your needs?
So does that mean I don't like the 5D Mark III?
No, not at all. I think it is a great camera. The shooting ISO at speeds up to 3200 is great for event photography and I think the AF improvement will make many event shooters go with the 5D3 (since 1D4 is only good up to about 1600iso). The new fancy functions are plus and although I would probably hardly use them it's nice to have. I still consider the 5D3 a prosumer camera and not a professional camera due to its built quality and slow shutter speed. It claims 6FPS, but it is still slower than the 7D nevermind the 1D4. I also felt the 1D4's battery strength is more meant for professional photographers. 5D3 can shoot about 600 RAW photographs with dual batteries (with the optional battery grip), while 1D4 can shoot 1500 RAW photos. That's an amazing difference especially if you are on the road or in an intense situation where you don't want to find yourself fiddling to replace your batteries. As well, as mentioned previously, I hate optional battery grips. Unless canon changes the design for their optional battery grip with the 5D3, or else it's definitely not a comparison with 1D4's built in battery grip.
The Full Frame Vs. Cropped Sensor question?
I never really understood why some photographers are so stubborn with Full Frame cameras? In a way I just think its more an image than really something that provides better pictures. True, with FF, this allows great pixel sizes and thus bettersince cropped sensors loose about a stop roughly. But remember, with a cropped sensor you are also shooting at shorter focal lengths when compared to a FF camera.
Also one thing you must remember with cropped sensors because it tends to have smaller pixel sizes, that for print is a good thing. Meaning that the pictures come out finer with higher detail. As for ISO issues, I don't mind that their will be tend to have more noise at high ISO compared to a similar camera at FF. I am a studio or portrait photographer and it's very rare that I hit ISO over 400.
As for some photographers stating that they can never get it right with a cropped sensor due to the change in focal length, well that is really a personal problem. I can only speak for myself, but framing wise, I use my eyes and not numbers. A lot of "professional photographers" use focal lengths to decide their framing, I don't. I think this has to do with the fact that I am not a Prime Lens shooter. It's like people always say you need to use a prime 85mm for portraiture but honestly if you look at some pros that are famous for portraiture, you will notice in their metadata that rarely do they shoot at 85? In fact most shoot more towards 90mm-110mm range. So I don't really get this must shoot at 35 or must shoot at 85 rule of thumb. Just sounds like nonsense. The only prime I use is really a 50mm and that's only for street photography/photo-journalism.
So to conclude, I don't find a difference using FF or APS-H, APS-C maybe but not with APS-H. But mind you I am a studio portrait photographer and at the most at times a photo-journalist. So for you sport shooters, macro shooters, product photographers... I can't really speak for you all.
I probably haven't covered everything, but you are more than free to contact me if you have any questions...
For more about sensor size and pixel size please visit this site...