5d3 vs 6d is a tough choice for me, if I were given either to use regularly for free and could not sell I'm not sure what I would pick.
-5d3 clearly has overall better AF, but on the other hand I can't put in a high precision focusing screen meaning I can't MF fast lenses accurately through viewfinder (or see what I am truly AFing); 6D center point also rated as being able to focus in lower light than 5d3 per Canon specs.
-I like the joystick on 5d3, but programming the pad on 6d to move AF points works also with a bit less comfort.
-I like the image quality of 5d3, but 6d has better high ISO performance.
-The dual card slots and 1/8000 shutter speed on 5d3 are a nice bonus I'd definitely use, but then again 6d has gps/wifi at no extra cost; though I'd rather have the fast shutter and dual cards than gps/wifi, fast shutter might reduce my usage of ND filters in daylight with fast lenses wide open.
I would like to say the 5d3 is a clear cut upgrade from 6D but there are a important few areas where the 6D exceeds the 5d3. Hopefully 5d4 will rectify these issues in all areas so I'd consider upgrading to it, as right now the disadvantages of the 5d3 prevent me from considering an upgrade...
LOL...really? I can't believe what I'm hearing GPS/WiFi are more important in choosing between 5D3 & 6D, LOL . You made my morning
Did you read my post? It does not appear so.
If I'm a wedding shooter, 5D III is clearly a winner. I have 4 friends(PRO wedding shooters), none of them carry 6D. Combined, they have eight 5DIII & six 1dx.
And, what does this mean to the total pool of wedding photographers which is multitudes greater than 4? Are you saying your friends are unable to shoot a wedding with a 5D2 or 6D? What did they do before the 5D3 came out? My guess is use the 5D2, which has worse autofocus than the 6D. I would be very concerned about the skill level of a professional unable to shoot a high quality wedding with a 6D.
The 1DX I would use no contest over the 6D as it dominates in all aspects, but I cannot yet justify the cost of two 1DX bodies when 6D is doing the job currently. I could justify two 5D4 bodies, but only if Canon does not gimp them by removing ability to interchange focus screens as they did with the 5D3.
With all focus points below, why MF? With just 41 combination of dual & cross type, recompose the shot is almost down to zero = less miss shots, even with f1.2 lenses.
Focus & recompose at f/1.2 will not acquire exact focus due to the thin DOF. While the 5d3 has a ton of focal points, often none of them are exactly where the eye would be in thin DOF portrait shots in either landscape or portrait orientations. Hence there is no way to truly focus properly for thin DOF portraits on the 5D3 aside from MF in Live View, which requires a tripod; you can spray&pray or recompose and hope it comes out okay, but I'd rather get it right the first time. The 6D comes stock with the same screen the 5D3 has stock, and they are both terrible for MFing fast lenses compared to the Ec-S/Eg-S screen which can be used on the 1DX/6D - but not the 5D3.
1. How do you MF in live wedding when your subjects are moving around?
You don't MF when you are capturing guests moving around. You MF for precise focus when doing shallow DOF portraits with bride/groom which are some of the most important shots of the whole wedding. 5d3's MF capabilities are very weak since there is no way to see true DOF with fast lenses unlike the 1DX and 6D with high precision screen. Even when using autofocus with fast lenses the high precision screen better shows what is in focus and what is not prior to taking the photo than the stock screen. For lots of motion I would center point focus in AI Servo and crop afterwards when needed.
2. At what high ISO does 6D is better than 5DIII?
I'd say it starts to becomes noticeable at 6400, which can be necessary at low light venues.
3. Assuming 6D center AF focus faster than 5DIII in -3EV condtion, would you delivery 12800ISO photos to your clients?
Not usually, though delivering a 12800 ISO photo is better than no photo. However, this is why I use f/1.2-f/1.4 primes... which once again, cannot be MF'd properly through the viewfinder on a 5d3 due to Canon obviously gimping the 5d3 on purpose to differentiate it from 1DX. Canon literally screwed a thin plate over where you would access the focus screen on the 5d3, but more problematicly removed the metering options for high precision screens out of the C.Fn settings - meaning if you change focus screens on 5d3, you void the warranty and your metering will be off.
The bottom line is, I don't want to give up the ability to MF my fast lenses through the viewfinder, and I also think the 6D autofocus is sufficient for most events (sports excluded, where I would rather use a 1DX).