Canon 5D Mark II focus question

Started Apr 11, 2013 | Discussions thread
Keith Z Leonard Veteran Member • Posts: 6,061
Re: Canon 5D Mark II focus question
1

hotdog321 wrote:

Well, it's not the camera. Anytime you shoot wide open you are going to get a certain number of "clinkers." The subject moves, or you move, or the camera shakes, or you just slightly miss the critical focus on the eye.

I shoot professionally with two 5DII. For critically tight headshots, I use the center point focus, one shot, single shooting. I focus on the nearest eye, reframe, shoot. Then refocus, reframe, shoot. And repeat and repeat and repeat until I'm sure I've nailed it.

Actually, it is the camera, the inability to have consistent output from the AF system is entirely the camera's doing.  Not to say that it's bad at it, just that if you do the same thing 50 times and get 50 different results, that's a bad sign.

I will agree that shooting wide open lends towards issues though, with the camera, with technique, and with chaos theory.

1.  The camera - maybe MFA your primes, the center AF point is better in all Canon cameras, but the 5Dmk2 is especially so given that it is the only cross type AF point.  The 5Dmk3 is better here due to the 41 cross type AF points, you can more than likely get a pretty reliable AF point over your focus area while framing as intended.

2.  Focus and recompose shifts the plane of focus which can be enough to throw an in focus shot out of focus when the depth of field is super thin.  Consider minimizing the shift and shifting your body in parallel to the focal plane as much as you can while minimizing the rotational aspect of it.  As hotdog points out try taking multiples as you will have some natural variation from both the AF system accuracy and your motions.

3.  Chaos theory, sufficiently complex systems yield occasional unexpected results.  Even if you do everything perfectly if your subject moves even a little bit between focus lock and recompose/shutter release you can have an out of focus shot when you are shooting DOF of only 1" or so.  The 85L @ 1.2 comes to mind here.    Another reason the 5dmk3 could be better, you can select an AF point over the eye, use AI Servo drive and fire off a burst.  This can increase your keeper rate in that one of those will likely be in good focus.

Focus/recompose can be very useful, it's very quick, a bit quicker than moving your AF point around, so it's just fine when you know you'll have enough DOF, like shooting f4 or f5.6 etc...but it can bite you when shooting very thin DOF.  There is a reason the 5Dmk3 exists, nothing wrong with the mk2, but they make improvements because they help sell more cameras.

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