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Thread: 7D 19 point autofocus - what's the point?

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    7D 19 point autofocus - what's the point?

    I typically always use the single center point for autofocus, however there are times when multi point is usefull.

    Yet from what i've experienced, the default Auto select 19 point AF is dreadfull.

    It seems to always front focus.


    An example:

    Photo 1 - Auto select 19 point AF


    50% crop




    Photo 2 - Single Point


    50% crop



    Shots were taken on a tripod with cable release, 1/800s, shot wide open (f/4) to help show focus issues.


    My only explanation is that because there are so many active focus points searching for a lock, if one point is only going to be correct only 90% of the time (for arguements sake), then you only have a 13.5% chance of all of the 19 points being correct with each shot.

    But yeah i dunno.

    Is this just how it is supposed to be? useless?

    thanks
    Last edited by pmack; 05-03-2011 at 3:02pm.

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    I'm not sure of what you are trying to say with all those percentages? Anyway, in any focus mode the camera will be trying to achieve focus on the closest thing it can find on ANY of the focus points which looks like what has happened with your example. The first is focussed closer because the camera has found something closer to focus on. In the second you have limited where it can search to just one point and forced it to focus where you want.

    For that reason most recommend not using 19pt auto and selecting something more narrow like zone selection or point expansion which are my favourites.
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    Moderately Underexposed I @ M's Avatar
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    In photo 2, why is the crop showing us a tree that is not under the centre focus point used and would appear to be in front of where the camera should have focussed?
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    Quote Originally Posted by etherial View Post
    in any focus mode the camera will be trying to achieve focus on the closest thing it can find on ANY of the focus points which looks like what has happened with your example. The first is focussed closer because the camera has found something closer to focus on. In the second you have limited where it can search to just one point and forced it to focus where you want.

    For that reason most recommend not using 19pt auto and selecting something more narrow like zone selection or point expansion which are my favourites.
    errrrm no there is nothing in focus in the first shot
    (Did you not look at the photo i posted?)

    and the point about the percentages was that any errors are exaggerated when you use multiple autofocus opints, as if just one of the 19 points gives a false reading, if this false reading gives a closer distance, then this false reading will be used for the focus, even if the 18 other points functioned correctly.

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    Quote Originally Posted by I @ M View Post
    In photo 2, why is the crop showing us a tree that is not under the centre focus point used and would appear to be in front of where the camera should have focussed?
    Look to the left of the tree in the crop, it's covers the same area that the focus point is on. I've just cropped a bit to the right.
    But anyway it is irrelevant, the image may as well be a brick wall, this is ~500 meters away. when one house is in focus, just about all of them are.
    the 1st image has focused between those two trees in the forground (10 meters away), and the rest of the image (500 meters away).
    so if there was a bee somewhere in between, it would probably be in focus, but i highly doubt the camera picked up any insects no more than a pixel in size...
    Last edited by pmack; 05-03-2011 at 5:13pm.

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    Moderately Underexposed I @ M's Avatar
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    In the second example where you have placed the centre focus point as the only focus point in use I would have expected the tree that seems to have filled a large amount of that focus point ( in the full photo at least ) to be substantially sharper than the house behind it yet we are unable to see it in the crop.

    As for the first photo there appears to be an extremely large depth of field between the focus points that seem to be in use and searching for something to lock focus on.
    I don't think that a scene like this is one in which the camera should be allowed to get it right as far as focus goes.
    The real benefits of having multiple focus points in a situation comes from being able to select one of those 19 points and use it for your composition without having to frame, focus, recompose and shoot. Canon bodies can do that can't they? Nikon manage it with 51 points and have a similar setup where using predictive tracking of objects using the camera chosen points is best suited to moving objects and particularly those that are moving towards the camera.
    Last edited by I @ M; 05-03-2011 at 5:14pm.

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    Quote Originally Posted by I @ M View Post
    In the second example where you have placed the centre focus point as the only focus point in use I would have expected the tree that seems to have filled a large amount of that focus point ( in the full photo at least ) to be substantially sharper than the house behind it yet we are unable to see it in the crop.
    huh? no. in the second photo, everything on the hill is in focus, both the trees and houses.
    At 500 meters, your DOF (even af f/4), is relatively huge.
    in the first photo, nothing on the hill is in focus. neither tree or house.

    Quote Originally Posted by I @ M View Post
    As for the first photo there appears to be an extremely large depth of field between the focus points that seem to be in use and searching for something to lock focus on.
    as i said, this is a long way away, it might as well be a flat image. none of the focus points are correct as not one tree or house on that hill is in focus.


    Quote Originally Posted by I @ M View Post
    I don't think that a scene like this is one in which the camera should be allowed to get it right as far as focus goes.
    The real benefits of having multiple focus points in a situation comes from being able to select one of those 19 points and use it for your composition without having to frame, focus, recompose and shoot. Canon bodies can do that can't they? Nikon manage it with 51 points and have a similar setup where using predictive tracking of objects using the camera chosen points is best suited to moving objects and particularly those that are moving towards the camera.
    yes i agree that that is one of the main benefits of the multiple points (selecting your own points), but that is not an excuse for the camera not being able to focus when all points are active. As for saying this is a scene shich is should not "be allowed to get it right", come on are you serious? this is the most simple of subject matters.
    Last edited by pmack; 05-03-2011 at 5:29pm.

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    Have you tested your lens using a focus test chart to see if it is focusing correctly? You might just find you need to do some micro-adjustments for the lens and the AF, on the 7D. I had to do so with me 70-200 on my D3, as it was front focusing. Once the micro adjustments to the AF system were done it is spot on.
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    Quote Originally Posted by ricktas View Post
    Have you tested your lens using a focus test chart to see if it is focusing correctly? You might just find you need to do some micro-adjustments for the lens and the AF, on the 7D. I had to do so with me 70-200 on my D3, as it was front focusing. Once the micro adjustments to the AF system were done it is spot on.
    I have not used a chart as such, however as it focuses correctly with the center point, micro adjustments will not help this issue.
    Last edited by pmack; 05-03-2011 at 5:47pm.

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    Administrator ricktas's Avatar
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    OK, was just asking!

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    Moderately Underexposed I @ M's Avatar
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    Quote Originally Posted by pmack View Post
    huh? no. in the second photo, everything on the hill is in focus, both the trees and houses.
    At 500 meters, your DOF (even af f/4), is relatively huge.
    Whilst the DOF ( even at F/4 ) may be large at that distance I would hesitate to say that everything is in focus, even of a pretty soft looking image like this there appear to be parts that are better focussed than others.

    Quote Originally Posted by pmack View Post
    in the first photo, nothing on the hill is in focus. neither tree or house.
    Quite possibly nothing on the hill is in focus but to me the branches of the gum tree intruding into the bottom r/h corner of the pic look substantially more in focus than the rest of the elements in the image. Perhaps that is where the focus locked when the camera was left to choose the point to focus on.
    Perhaps one of those branches was blown into the focus area .



    Quote Originally Posted by pmack View Post
    yes i agree that that is one of the main benefits of the multiple points (selecting your own points), but that is not an excuse for the camera not being able to focus when all points are active. As for saying this is a scene shich is should not "be allowed to get it right", come on are you serious? this is the most simple of subject matters.
    Yes, I am serious, and that "simple scene" is obviously one that is not so simple for the camera to get correct. It just is not the type of scene where the camera should be allowed to override user selectable focus points.
    Whilst modern DSLR cameras are extremely technologically advanced and accurate in a great number of cases they do require user input to determine the best method of obtaining an image.
    Focus and when to use which method are simply one more area that need to be learned thoroughly and applied appropriately because to put it quite simply the camera does not know which particular part of the scene that you want in focus without being told.
    Last edited by I @ M; 05-03-2011 at 5:58pm.

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    Quote Originally Posted by ricktas View Post
    OK, was just asking!
    all good. personally i think it is just a poor algorithm that canon use when multiple points are active.
    it's like the camera just gets confused, too many choices and so it gives a result that is wrong for all focus points.
    very frustrating (you can probably tell from my replies I am very frustrated! I am frustrated. fact! )
    Last edited by pmack; 05-03-2011 at 6:01pm.

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    Ausphotography Regular agb's Avatar
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    There is no doubt that you are not a happy 7D owner pmack, as I think this is your third thread about focus with this camera, and it seems to me that you are no nearer to being satisfied. It is a pity that you cannot get with some other users of this model and compare notes about its functions and results. I have one, and I set it up to my own satisfaction after reading some articles about other users and how they have set it up, and can say that I am very happy with the focus that I achieve. If I lived closer to you I would be happy to share notes and let you have a go with mine, sorry I am too far away.
    Mind you I disabled the 19point ( ) focus as soon as I bought the camera and have never used it that way. I have however used spot, single , expanded and zone , and have used most of the 19 points to achieve focus, usually singly or spot moving my focus point with the joy stick as required. I have never had an issue. I have it set to back button focus with the * button, and I have the AF-on button set to lock metering, so the shutter button only meters and takes the photo for me.

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    Quote Originally Posted by I @ M View Post
    Whilst the DOF ( even at F/4 ) may be large at that distance I would hesitate to say that everything is in focus, even of a pretty soft looking image like this there appear to be parts that are better focussed than others.
    two objects at the same distance can appear to be focused differently due to colours and shape giving a different perceived sharpness, so not related to focus, but easily confused with. I can assure you from looking at the original file @100%, all of the hill in focus, perhaps at the very top it starts to fall out of the DOF marginally.
    can we not digress?

    Quote Originally Posted by I @ M View Post
    Quite possibly nothing on the hill is in focus but to me the branches of the gum tree intruding into the bottom r/h corner of the pic look substantially more in focus than the rest of the elements in the image. Perhaps that is where the focus locked when the camera was left to choose the point to focus on.
    Perhaps one of those branches was blown into the focus area .
    nope the tree in the foreground on the bottom right is not in focus.
    i would have taken test images without trees to distract the camera (or forum repliers), but that would have meant taking a photo of a friends house, and they may have found it kinda creepy posting that on the web... haha.

    Quote Originally Posted by I @ M View Post
    Yes, I am serious, and that "simple scene" is obviously one that is not so simple for the camera to get correct. It just is not the type of scene where the camera should be allowed to override user selectable focus points.
    Whilst modern DSLR cameras are extremely technologically advanced and accurate in a great number of cases they do require user input to determine the best method of obtaining an image.
    Focus and when to use which method are simply one more area that need to be learned thoroughly and applied appropriately because to put it quite simply the camera does not know which particular part of the scene that you want in focus without being told.
    The camera is not overiding anything.
    If some kid picks up an SLR for the first time, puts it in full auto mode, and half presses the shutter button, if a red square comes up over an object, that object should be in focus IMO.
    In the image i took, the camera has focussed in the middle of the valley, into empty space.
    It really should not require user input to overide a retardedly stupid decision that was made by the camera IMO.

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    Hi agb,
    yes this is my third question about autofocus with this camera (all about different issues though), but I was hoping I would get others telling me if their camera acts like this or not, rather than argueing about nothing!
    I think i said in the other thread that i was going to end up sending the camera to canon anyway to get it checked out, but i just wanted to hear experience/opinions of others first.

    Regarding the 19 point, realistically the only time i ever enable all points is when i have an ultra wide angle and am taking photos of moving objects close up. So in which case, it does not need to perform like you would expect it to perform in my test (~infinity focus).
    So the only reason i am posting this topic, is just to find out if this is normal behaviour.
    So if the camera can't handle having 19 points active (as I belive this topic prooves), then how much can you trust it when you reduce it to 9 points? (rhetorical question as i realise you personally do not have any problems in other zones)
    Last edited by pmack; 05-03-2011 at 6:48pm.

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    Moderately Underexposed I @ M's Avatar
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    Quote Originally Posted by pmack View Post
    errrrm no there is nothing in focus in the first shot
    (Did you not look at the photo i posted?)
    Quote Originally Posted by pmack View Post
    In the image i took, the camera has focussed in the middle of the valley, into empty space.
    I am starting to have troubles with this, first you say that there is nothing in focus in the pic and then you say that the camera has focussed half way in.

    You can't have it both ways, either the camera focussed or it didn't and I still reiterate that focus and the correct methods of when and where to apply it are things that need to be learned and not left up to the camera.

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    Quote Originally Posted by I @ M View Post
    I am starting to have troubles with this, first you say that there is nothing in focus in the pic and then you say that the camera has focussed half way in.

    You can't have it both ways
    Yes you can. There is no visible object in focus.
    The camera has told the lens to select a focus point that is somewhere between the trees in the foreground (10 meters away), and the hill which is 500 meters away.
    so it appears to have focused somewhere between 10-500meters, which is what i mean by half way. half way across the valley.

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    Quote Originally Posted by pmack View Post
    Hi agb,
    yes this is my third question about autofocus with this camera (all about different issues though), but I was hoping I would get others telling me if their camera acts like this or not, rather than argueing about nothing!
    I think i said in the other thread that i was going to end up sending the camera to canon anyway to get it checked out, but i just wanted to hear experience/opinions of others first.
    Obviously you aren't happy with this camera and have made your mind up what you think. People here are just trying to help you but it seems you don't want to listen. Do some decent focus tests with a focus chart (there are plenty of examples here about microadjustment and how much difference it can make). If you tick all the boxes and still aren't happy send it to Canon or sell it!

    If you don't want to listen to people trying to help you and just want to argue everything, don't bother asking the question!

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    Moderately Underexposed I @ M's Avatar
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    pmack, either the camera focussed or it didn't.
    If, as you have said nothing is in focus then the camera failed to achieve focus.
    You have said that the camera focussed "somewhere between the trees in the foreground (10 meters away), and the hill which is 500 meters away" so therefore something must be in focus.

    How many attempts did you have at allowing the camera to achieve focus based on the camera body's guesstimation of a focus point?
    How many attempts did you have at allowing the camera to accurately focus when you selected the point to focus on?

    Quote Originally Posted by pmack View Post
    The camera has told the lens to select a focus point
    No, the lens does not select a focus point, the camera body is wholly and solely responsible for determining focus ( autofocus ) from the information about light, contrast and colour that is transmitted through the lens.

    As a final comment on this issue, I urge you to set up a definitive and technical focus test under controlled conditions with repeated examples and then determine the outcome for your self, either that or send the camera to Canon for testing and repair / rectification so that it falls within their specified tolerance.
    Of course, the repair / rectification will either be free if outside of tolerances and the camera is under a local warranty or you will have to expect to pay for adjustments if the camera is out of warranty period or is a grey imported body.
    Last edited by I @ M; 05-03-2011 at 7:20pm.

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    Quote Originally Posted by etherial View Post
    Obviously you aren't happy with this camera and have made your mind up what you think. People here are just trying to help you but it seems you don't want to listen. Do some decent focus tests with a focus chart (there are plenty of examples here about microadjustment and how much difference it can make). If you tick all the boxes and still aren't happy send it to Canon or sell it!

    If you don't want to listen to people trying to help you and just want to argue everything, don't bother asking the question!
    once again, are you actually following what is going on in this thread?
    I'll just post my response to ricktas who has already suggested this
    "as it focuses correctly with the center point, micro adjustments will not help this issue"

    I'm not arguing for fun, i'm arguing to keep suggestions valid and usefull.
    If I see that someone says something wrong, i'll say it. a spade is a spade, etc.

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