5DMiii AF Selection: what do you use and when?

Discussion in 'Canon Cameras' started by Jade16, Sep 28, 2015.

  1. Jade16

    Jade16 TPF Noob!

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    For shooting outdoor (non moving/seated) Family portraits which AF selection point patterns do you use when shooting:
    A. Individual
    B. Couples
    C. Family of 4 or 5

    For example, I might use a Single Point AF or Single Point Spot AF for an individual, but I may use a Zone AF (cluster of AF points) for a family. I am interested in hearing what others do.

    And what about when the family is moving, walking around, running, jumping, etc. would the same methods apply?

    Here are the different options of AF point patterns:
    -Single point Spot
    -Single point
    -AF point expansion (manual selection)
    - AF point expansion (manual selection, surrounding points)
    - Zone AF
    -61 point automatic selection (all points are used to focus)

    Any help would be greatly appreciated!


     
  2. ronlane

    ronlane What's next? Supporting Member

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    I would use Single point spot (the smallest one) on both A & B and possibly C if I was posing them and made sure that they were all on the same focal plane.

    For moving subjects, I honestly would use the SPS or SP with AI Servo, so that the camera tracks the eye.
     
  3. TCampbell

    TCampbell Been spending a lot of time on here!

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    I would usually use single point on all of these. Since you are asking about non-moving subjects I'm thinking perhaps you don't understand the reasoning behind each mode.

    Single point is the standard "go to" mode to choose when you want to control the focus distance to your subject.

    So why have "spot" and "expansion" modes? The answer is "focus contrast".

    In order for the camera to focus, it needs something with a bit of contrast. If you point your camera (just as an example) to the middle of a clear blue sky and ask it to focus, it will probably give up on you because there's nothing of any contrast for it to use... the blue looks identical whether the camera lens is focused or not... when focusing the lens doesn't change the result, there's not enough contrast to focus.

    You're unlikely to ever need to focus on something with as little contrast as a plain blue sky... but if you are trying to focus on something with very weak contrast, you can help the camera focus faster by "expanding" the area in which the camera can search for contrast. Hence the two AF point "expansion" modes. Those are STILL considered "single point" modes except that they get to borrow the focus points around them to try to broaden the search for adequate contrast. In other words, when shooting subjects that have poor contrast (plain surfaces, etc.) then broadening the area that the camera uses to find contrast by using an "expansion" mode will help the camera focus faster.

    But there is a downside to broadening the AF area... it's possible that if the area is too big then some things within that focused area will be closer than others. With a shallow depth of field, this might cause the camera to lock on to something we wish it had NOT used for focus... and miss focus on the details we care about.

    For example... suppose I want a detail of a subject's face and I want focus on their eye. The challenges are that the "eye" is slightly farther away from the brow-arch or nose. If my focus area is too large, the camera might lock focus on the eyebrow (which is closer than the eye) and render the eye itself to be slightly soft. I can avoid this by switching to "spot" AF mode. It's the same single-point mode... except it reduces the area used to lock focus to be even smaller than standard single-point AF.

    The challenge with "spot" AF is that it will have a more difficult time focusing if you try to use it on a subject with very poor contrast. An eye actually does have quite a bit of contrast so it's likely to work well in that situation.

    "Zone" focus is simply allowing the camera to auto-select the AF point... except you limit the search to a specific "zone" of points rather than use any of the 61 points the camera has available. I sometimes use this if I'm shooting quickly and know roughly where I intend to place my subject and want to make sure I have the AF points available in that zone (so I don't have to precisely place my single AF point). Also note that the camera tends to go for the AF point with the closest focusing distance so make sure you don't have anything in that zone which is closer to the camera lens then your intended subject.

    And lastly the there's full 61 point auto-select...

    The Canon system is normally programmed to identify the AF point which can achieve focus at the closet focusing distance. This is usually not desirable because you don't have as much control. But the 5D III has an exception when using "AI Servo" focus.

    When you use full 61-point mode with the "AI Focus" method the camera will let you set an "initial" focus point by highlighting a single AF box (which you can move around -- you get to choose which of the 61 points will be the "initial" point.) Then... following the various intelligent tracking & recognition (iTR) algorithms, the camera will "follow" whatever subject you selected as the initial point as that subject moves around the frame (again... the iTR is tunable ... you get to pick the mode and adjust parameters to determine how "sticky" it will be to your subject or if it will be willing to jump to a new subject if it thinks the original subject was lost.) This type of focus system is really intended for action photography and not very useful for portrait photography.
     
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  4. EIngerson

    EIngerson Been spending a lot of time on here!

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    Thanks Tim. Always good take away from your responses.
     
  5. Jade16

    Jade16 TPF Noob!

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    thank you very much! very helpful. I tend to place the focus point over the eye closest to me. I have observed in this forum that some prefer to place the focal point in between the eyes (but I would assume that this latter method would not provide the contrast that would be ideal for focus). Thoughts?
     
  6. Jade16

    Jade16 TPF Noob!

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    and I am not quite sure what you mean by this..can you please elaborate? what did you mean by controlling the focus distance to your subject"?
     
  7. TCampbell

    TCampbell Been spending a lot of time on here!

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    When you use auto-select modes or even zone-modes the camera chooses the point. The major difference between regular "auto" AF selection and "zone" AF selection is that in full auto selection it can choose any point it wants... whereas in "zone" mode it can choose any point it wants as long as it's a point in the "zone" you choose (the zone is a cluster of AF points).

    But this means that there's a possibility that the camera may lock focus on something OTHER than your intended focus target. With full "auto" AF selection mode (where the camera can choose any point) it much more likely. With "zone" mode it's possible... but less likely as long as you pick a zone (cluster of AF points) in the area where you intend to compose your subject in the frame.

    When you select single point mode, you pick THE point that the camera will use and it has no choice. It cannot pick a wrong AF point. Now it's just up to you to make sure keep that point on your intended subject (if it's a person... this is probably their eye.)

    The other modes ("spot af", "expanded af", and "surround af" are all variations on the single point mode depending on if you have a low or high contrast focus subject and also depending on if your focus subject is a big target or tiny target. "Spot AF" is, of course, better for tiny targets but it does require that the target offer adequate contrast to lock focus. "Surround AF" uses a much larger target (not good for tiny targets) but it can still manage to lock focus on targets with poor contrast.
     
  8. Jade16

    Jade16 TPF Noob!

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    thank you!!
     

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