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Thread: Lots and lots of auto focus points... ?

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    Member achee's Avatar
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    Lots and lots of auto focus points... ?

    Hi guys!

    I was wondering if someone could explain to me... what is the advantage of having lots of focus points? Am I missing the point bacause my genres of photography don't call for lots of AF points, or I'm not making the most of my camera features?

    When I say lots, I mean anything more than about... 9 or so.


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    Ausphotography Regular livio's Avatar
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    Hmm I don't know but more than 9 gives you choice of course this will depend greatly on what it is you photograph. Lets say portraits in a studio few focus points will do because I would mostly be interested in the eyes and because I'm in fairly close it will mean that I don't need all the focus points. If I am doing a product shoot however that will change depending on the product and the mix. If I am doing bands or sport hell I want as many focus points as I can get because I dont have time to compose each frame and the rate of change is is faster than I can manually focus on. If the camera is in Continuous Auto Focus and screaming through at 8 or more frames per second I want the camera to choose and then I can decide which is the best. Remember that the difference between a great photo and good one is very subtle. Even with all focus points active you are not guaranteed a good shot however the probability is stached in your favour.

    Kind Regards
    Livio

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    Moderately Underexposed I @ M's Avatar
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    Quote Originally Posted by achee View Post
    or I'm not making the most of my camera features?
    That would be about it I reckon.

    I can think of at least two reasons for any known genre where the use of more than just the centre or one focus point is a great aid to composition and accuracy in general.
    Andrew
    Nikon, Fuji, Nikkor, Sigma, Tamron, Tokina and too many other bits and pieces to list.



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    Administrator ricktas's Avatar
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    disclaimer: I might be wrong here**

    I also believe that cameras that have '3d focus tracking' use these focus points as part of the tracking mechanism when activated. I reckon they kick in and help the focus system track a moving object, rather than just the single focus point doing all the work. Therefore more focus points ensure a more accurate focus tracking on moving objects.
    "It is one thing to make a picture of what a person looks like, it is another thing to make a portrait of who they are" - Paul Caponigro

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    Ausphotography Regular swifty's Avatar
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    I believe Rick is correct. Continuous AF tracking is one area where many AF points would be advantageous for accuracy.
    Personally I don't need that many, and by that many I mean like 50+
    But what I would like is a wider spread of them and more accurate/sensitive ones.
    AF also tracks faster with fewer AF points active (less info to process). AF patterns can be configured so you dont always have to have all AF points active. You choose the config that best fits your subject.
    But with the march of CPU processing power, it'll certainly keep up with the increasing number of AF points and hence increasing amount of info to process. We're now starting to see embedded PDAF sensors on the imaging sensor working in conjunction with contrast AF with higher and higher refresh rates.
    This should improve focus speed and accuracy that'll benefit any genre.
    Nikon FX

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    1) OK, so lots of focus points is good if the subject is moving too quickly to do focus/recompose, and/or if you're using AF tracking. In these cases the photographer doesn't have time to manually choose what to focus on, so the intention is that the camera chooses and the more AF points to more chance the camera chooses right. Right?

    2) If the subject isn't moving, say, you're composing a still scene on a tripod, you can manually select an area of the scene to focus on without having to move the camera around, so the more AF points the more chance there will be one in the right place... that's the advantage, right?

    3) Oh, and I just thought of another possible advantage - assuming the best part of the scene is to be in focus, more AF points -> more contrast comparisons -> more data to base the focus on. This could be useful in low light or for a low contrast subject.

    (I've been reading about the new Canon 6D... 11 AF points compared to 5D III's 61)

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    Administrator ricktas's Avatar
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    1) 3d tracking is designed to lock onto and follow a moving target. So say you are shooting a tennis match, you can half press the shutter and lock onto a player. It now does not matter if the player moves left, right, forward, backward on the court, the 3d tracking will automatically follow them and keep them in focus. It uses more than one of the focus points to keep 'watch' on the subject and allow the auto-focus system to track them. So the more focus points, the more accurate the tracking.

    2) Yes. I often set my camera up on a tripod for landscapes and then choose the focus point (single point focus) that I want to use for the scene. Sometimes your composition is such that you want to not move the actual camera body, but choose a particular thing in the scene the focus on. The more focus points, the more you have a chance of having one over your main subject.

    3) Yes

    So whilst more focus points can be great for particular genre/types of photography, there is not a magic number of focus points that is the correct number to have. Remember that photography is nearly 200 years old now and multiple focus points have really only been around since the 1970's and lots of superb photos have been taken without the use of the tech we have now.

    Yes it is nice to have, but it is not necessary to have, to take great photos.
    Last edited by ricktas; 18-09-2012 at 7:10am.

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    Ausphotography Regular swifty's Avatar
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    Achee, have you shot wide open on f1.4 lenses or faster at close range.
    The DOF is very shallow and using the centre AF wand recompose just doesn't work.
    You'd normally choose the closest AF point to where u want to focus on to minimize change in composition before shooting. That's my number 1 need for multiple AF points, particularly more spaced out ones. But if there are too many, it takes too long to select the right one and u might miss the moment.

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    No, not much; most of my shallow DOF photos would be taken at 100 - 200mm f/2.8, so focus / recompose seems to work. I see your point, though. Also, I think the UI on my camera doesn't make it easy to quickly select an AF point!

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