My 5D II and 5D III are fantastic.
You might want to read this article: http://www.lensrentals.com/blog/2008/12/this-lens-is-soft-and-other-myths
The 5D II supports auto-focus micro-adjustment... meaning you can test and fine-tune the focus accuracy on the camera -- which can be different for EACH lens you own.
When I test the camera using a focus-test chart it's bang-on accurate every time and with every lens I test. This is not to say that it will always be accurate with every lens. Every so often a single "copy" of a lens will be flawed. But the higher end the lens, the less likely that you'll encountered a flawed copy.
Here's the thing: DO NOT take ordinary pictures and use that as a test of camera focus accuracy. There are simply far too many reasons why a perfect camera & lens combination can end up with a soft image that having nothing to do with the camera.
If you want to test a camera, you have to isolate all those other causes. The camera has to be tested with camera on a tripod, using a stationary focus test chart (and there are parameters for how these have to be setup to have a valid test -- chart instructions usually explain how to establish a proper test distance which will vary based on the focal length of the lens). The conditions need to be controlled. If the camera & lens are soft under "controlled" conditions, then you (a) might have an issue and (b) you can usually isolate the specific cause to where you will know what needs to be addressed to correct the problem (and often it's something you can do yourself.)
There is nothing plaguing the 5D II.
There were huge complaints about the 5D II focus system... but the complaints were not about accuracy problems, they were largely about how a $2500 camera body ends up with the same basic focus system that they had on a $500 camera. When Canon released the 5D III they went all out on the focus system. The 5D III had one of the very best focus systems of any camera on the market when it was released (only the 1D X was better... and that system was only very fractionally better.)
There is a "story" behind how the 5D II ended up with that same basic focus system. I'd rather not share the story here because I have no way of knowing if it's true.
If you allow the camera to auto-select the AF point, then it is programmed to always select the point at which it can achieve a focus lock at the CLOSEST focusing distance to the camera. If you don't want it to do that, then tell it to pick a specific point (poke the AF point selection button, then use either the selection wheel on the front OR the navigator joystick on the back to select the AF point you want.)
If everything is used correctly and you STILL have a focus problem, you need to properly test the lens with a focus test chart and perform the auto-focus micro-adjustment. If you STILL have focus problems even after performing that (in properly controlled test conditions) then the culprit is likely the lens.
The reason it can be the lens has to do with "how" the phase-detect AF system works. It's possible to derive the correct focus position from merely one sample off the AF sensor. Due to the nature of "phase detection" the camera can determine if the focus is either in-phase vs. out-of-phase; if out-of-phase the camera knows which direction it needs to go (it knows if focus is too far vs. too close); and it actually knows precisely how far it needs to adjust. When the computer samples the focus point, it orders the lens to adjust by a specific amount which should send the lens to perfect focus every time. But if that lens has gear backlash then the lens can miss focus due to backlash issues -- that's a lens problem -- not a camera body problem.
Another way to test for issues with the phase-detect focus system is to switch to "live view" and test focus that way. Live view mode uses "contrast detect" auto-focus instead of "phase detect" auto-focus. Contrast detect is slower and requires that the camera iterate through numerous focus checks before it can be sure it's properly worked out focus... but due to the way it works, the camera cannot just "know" which way it needs to adjust -- nor how much of an adjustment is needed. So it has to keep re-sampling the image. This makes for a much slower system... but because it keeps refining and re-evaluating the focus, it tends to always nail the focus (eventually). Phase-detect will nail the focus much faster (it's near-instantaneous) IF everything is working correctly.
Tim Campbell
5D III, 5D IV, 60Da
