Missing Focus - AF (5DM3)

ding76uk said:
The depth of field is so small at f2 that it is bound to show limitations of any AF system. Does it miss all or just some?
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I stood still, took a couple of shots of a runner yesterday - missed both.

Also I frequently miss focus if I take a shot whilst walking towards someone else walking towards me - I have to walk slowly for this to work :)
 
i'm not an expert in this and my 7D has less fancy dials than that but a similar system.
do you use a single point of AF or a centralised pattern?
I would have thought that a single point would be less accurate than a small bank of 9 points in the centre area.
 
DizMatt said:
i'm not an expert in this and my 7D has less fancy dials than that but a similar system.
do you use a single point of AF or a centralised pattern?
I would have thought that a single point would be less accurate than a small bank of 9 points in the centre area.
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I was using the cross pattern (5 squares), and I have reduced the 61 points to those 3 strips it recommends in the article - I was using some of the left column points.
 
Just to point out the line of focus is always just slightly behind the person - so I haven't missed it completely - it's just not keeping up.
 
You know you can also increase sensitivity to movement in whatever "case" you use i.e. tracking sensitivity?
In the example you show (case type 2) sensitivity looks to be set quite low i.e. -1

Matt
 
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That camera and lens should be able to eat any servo-tracking subject easily with a very high hit-rate.

Summat is not right, could be all sorts of things. First thing to do is probably check and understand camera set up carefully, and technique.
 
MatBin said:
You know you can also increase sensitivity to movement in whatever "case" you use i.e. tracking sensitivity?
In the example you show (case type 2) sensitivity looks to be set quite low i.e. -1

Matt
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Thanks I hope something like this is the case, I will change the setting and play with it.
 
Dan, the others have touched on most of this already, but there are a number of things to consider when focusing:

  • your chosen lens - some lenses focus more slowly than others and this is particularly true of large aperture telephoto primes. It is possible that by the time the lens has managed to move its large chunk of glass, your target will have moved beyond the plane of critical focus - this would be notable when shooting with wider aperture. From what you've said, this could be a likely cause of the symptoms you've described. Test this by shooting in a similar manner, but with a zoom lens.
  • The nature of the movement - front to back movement can be more challenging often because the subject is filling the frame to a greater or lesser extent as you shoot, which can affect placement of your focus points. When I have shot catwalk shows for example I would generally expand my usual small single centre focus point to include one set of points either side and above
  • Tracking sensitivity - as has been mentioned, this can be adjusted to suit
This article may be helpful (it is about the 1DX but the focusing system is the same on the 5D MkIII) the download document is in the bottom left-hand corner: http://www.learn.usa.canon.com/resources/articles/2012/1dx_guidebook.shtml
 
Lindsay D said:
Dan, the others have touched on most of this already, but there are a number of things to consider when focusing:

  • your chosen lens - some lenses focus more slowly than others and this is particularly true of large aperture telephoto primes. It is possible that by the time the lens has managed to move its large chunk of glass, your target will have moved beyond the plane of critical focus - this would be notable when shooting with wider aperture. From what you've said, this could be a likely cause of the symptoms you've described. Test this by shooting in a similar manner, but with a zoom lens.
  • The nature of the movement - front to back movement can be more challenging often because the subject is filling the frame to a greater or lesser extent as you shoot, which can affect placement of your focus points. When I have shot catwalk shows for example I would generally expand my usual small single centre focus point to include one set of points either side and above
  • Tracking sensitivity - as has been mentioned, this can be adjusted to suit
This article may be helpful (it is about the 1DX but the focusing system is the same on the 5D MkIII) the download document is in the bottom left-hand corner: http://www.learn.usa.canon.com/resources/articles/2012/1dx_guidebook.shtml
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Lindsay I do not have a zoom lens - only primes, are they typically faster focussing than primes?

I found a few things that could have gone wrong

- MFD was set to 1.6 and not 0.9 - wouldn't have affected the runner - but there were other shots where I missed focus
- My camera was on single shot - not sure when I changed that, but I've had it on AI servo for a while and expected it to be still on, this is probably the most significant factor with the runner yesterday.
- I have now set acceleration and tracking sensitivity to max

I took some test shots.

These ones with single AF point selection, I felt I did a pretty good job with keep the focus on his face - but not all shots were perfectly focussed. Shutter speeds were 1/1000 - 1/2000 which should be plenty?

View attachment 9046 View attachment 9045 View attachment 9044 View attachment 9043 View attachment 9042
 
So it looks like - single point AF mode, getting the rest of my settings right and close attention to keeping the subject's face in the AF point will get me the best results - although not necessarily perfect.
 
dancook said:
So it looks like - single point AF mode, getting the rest of my settings right and close attention to keeping the subject's face in the AF point will get me the best results - although not necessarily perfect.
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Yes, it's usually down to settings and technique ;) You've just got to put the time in learning those, with the help of Canon's excellent white papers that Lindsay linked.

Use AI-Servo, not One-Shot or AI-Focus. I usually have focus acquisition on AF priority for the first shot, then drive speed; AF pattern and tracking sensitivity according to subject, usually centre-point with expansion points enabled. Back-button AF. YMMV.

Always pick up the subject early and get focus locked on before shooting. I find the hardest part is usually keeping that AF point really accurately nailed. If that's tricky, set tracking sensitivity to Slow.

I did a lot of AF tests with the 5D3 when it first came out and was frankly amazed at how good it was. A runner like yours, but reversing around cones, then stopping and then sprinting to camera. On continuous drive it would usually fill the buffer with 100% sharp shots. Lens was 70-200/2.8 Mk2, at 200mm f/2.8, though I'd be surprised if your 135/2 wasn't just as good for that. The focus doesn't actually have to move very far between shots.
 
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HoppyUK said:
Yes, it's usually down to settings and technique ;) You've just got to put the time in learning those, with the help of Canon's excellent white papers that Lindsay linked.

Use AI-Servo, not One-Shot or AI-Focus. I usually have focus acquisition on AF priority for the first shot, then drive speed; AF pattern and tracking sensitivity according to subject, usually centre-point with expansion points enabled. Back-button AF. YMMV.

Always pick up the subject early and get focus locked on before shooting. I find the hardest part is usually keeping that AF point really accurately nailed. If that's tricky, set tracking sensitivity to Slow.
Click to expand...

I set my camera up for back button focussing, using AI-Servo - so I can use it for both "single shot" and "continuous focussing" - I took it for granted it was on :D
 
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