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Thread: Issue w/ Focus

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    Default Issue w/ Focus

    AI Servo AF, Area Expansion is Set to Expanded, ISO 800, 1/800, F/8, Lens is 400 f/5.6 shot w/ 5DMII I am wondering if someone can help identify why the camera is focusing so far forward. Is it just that the shutter was released just too soon before the lens starts to move the focus?

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    Chris,
    There are a couple of possibilities.

    1) We don't know the time history of where the focus point was. If the focus point was in the background and moving to the bird because you moved the camera, the camera could be projecting the subject to focus on is moving toward the camera. Thus it set focus in front of the bird. Was the image made with the camera on a tripod? If not, and hand held, then your swaying could move the focus.

    2) you need focus microadjustment.

    If #2, out the camera and lens on a tripod, and focus on a high contrast object on a wall (be perpendicult to the wall). Now turn on live view, magnify the max, and use a cable release to half press the shutter button so the camera uses live view to focus. Do you see a change (the focus gets better)? If so, then you need a microfocus adjustment.

    Roger

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    Quote Originally Posted by Roger Clark View Post
    Chris,
    Roger
    Hi Roger,


    I kind of doubt it's a Microfocus Adjustment issue I checked the lens wide open against a tilted target when I first got the lens last year. Also, see this image I took two days after, it appears to be right on target. It is however in One-Shot AF mode tripod mounted. (see Exhibit B)

    A little bit of time history on the Heron photo. I saw the Heron on the shoreline and he took flight, I'm still very much a novice about BIF so I raised the camera up and took the photo hand held, as from what I've read on the BPN forums people think the 400mm is best used hand held for BIF. I don't know where the lens' "focus state" was prior to taking the shot, it could have been previously focused much closer. I am purely speculating since the focus error is so fa in front. But as you say if the time evolution was a lens track a BIF coming towards me this might account for the focus error.

    If on the other hand (and I am unsure if they are mutually exclusive) the problems was due to operator movement I must confuse I am stumped as I've heard also on these forums is that is BEST to use AI Focus for handheld shot for precisely the reason of camera operator movement.

    Exhibit B:

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    My camera, at least, can be set up so the shutter will not release until focus is locked, which is an extremely fast event, and I can't imagine a time delay between focus lock(AF aquisition) and shutter realease. I don't know about area expanded, but I think you need to have the AF on a single point. It can be the centerand other preselected positions as well. If you use a number of points the camera can only average them and come up with a point that may not be your subject. We are concerned primarily with the subject being in focus, and other element included by use of the DOF, so "expanded" is likely your problem. Regards~Bill
    Last edited by WIlliam Maroldo; 01-27-2011 at 02:22 AM.

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    Hi William,

    The area expansion refers to 6 invisible points around the central AF sensor that assist the central sensor in acquiring focus. I am assuming your using Nikon? I don't think AI Servo has the same function as you are describing.

    I have other shots of BIF that have what I think is the same issue as that as seen in pane #1 so I'd like to nail down why I am encountering the problem, or possibly what scenario I should test out to improve my technique.

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    Hi Chris, I currently shoot a Sony A850 and there are 3 choices for AF coverage; wide, spot, and local. My point was that if you used other than spot there might be problems. I am not clear what "AI Servo AF, Area Expansion is Set to Expanded, means, but my conjecture was that it may be the root of the problem. So what does it mean, and is it something only to do with assist points? regards~Bill

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    William,

    AI Servo is the focus mode and area expansion takes the 6 invisible focus points surrounding the center AF and uses them to help the center AF point lock on.

    I looked back through various threads and I recall reading Arash Hazeghi says he shot w/ the 5DMII shots in area expansion mode. I've checked his photo gallery and there a lot of BIF shots that are all in focus so I am inclined to think the mode is not the problem, but I will check w/ and w/o but I really think it is me that is issue.

    I am just wondering if someone has a more controlled/repeatable scenario that I can practice to hone this AF Focusing of BIF since my focus hit rate is low.
    Last edited by Chris Korman; 01-27-2011 at 03:27 PM. Reason: line breaks

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    Okay An addendum.

    I've mulled further through the BPN threads and have come across these two threads:

    http://www.birdphotographers.net/for...2635#post12635

    Which advocates turning off expansion mode.

    http://www.birdphotographers.net/for...-focus-for-BIF

    The place I go to photograph the heron there appears to be only one, so "real life" practice is kind of hard. So if there is an analogue to a BIF can someone point me towards, that would be appreciated.

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    Chris - I also shoot a 5DII. I most often shoot BIF utilizing center-point only selected and utilize the AF Expansion Assist points (CFn III-7) in AI Servo mode with the same 400mm f/5.6L lens - I can honestly say I've never had an issue getting sharp focus on BIF shots with this combination. About the only issues I have had are with the focus tracking in low light situations (i.e.), but it appears you have bright, direct light in your shot.

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    Thanks Jeff for the link to your photo of the owl. Good capture.

    How long had you been tracking the owl in the viewfinder? Were you shooting handheld? My guess is that your technique is such that you are already prefocusing or close to in focus, is this correct?

    Also do you "bump focus" as Jim Neiger says when you are tracking? Although he eschews the area expansion and uses a sole center point.

    Were you shooting in continuous burst mode? And did you capture multiple keepers? (I myself am rather trigger shy and that also may be a problem, for if I had only been holding down the shutter release a subsequent frame might have come into focus?)

    I think I may go out and photograph some fast vehicles to see if my technique or mode can improve.

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    Chris - In answer to your questons: The linked photo is the second shot in a burst (i.e. shooting continuos burst mode), but it is the first sharp one - subsequent shots are also sharp. It looks like the first shot was out of focus because the camera picked up some stands of grass a couple meters in front of the bird. I do use the "bump focusing" technique if I am having trouble keeping the focus locked.

  12. #12
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    Chris,
    I'm not familiar with the 5DII , but if it's at all like the 7D, you likely have a custom function (C.FnIII -2 on the 7D)that controls AI-servo and shutter release timing. I have a hunch you maybe have this set to "release" priority for the first shot, and/subsequent shots; if so the shutter can and will release immediately (whether focus has been acquired or not.

    Check the following custom function settings : AI Servo 1st/2nd image priority, and AI Servo AF Tracking Method (I don't know the exact number for these but they're likely on the C Fn. III menu (as they are on the 7D) Try setting the first of these to "Af Priority/Tracking priority" and the second to :" Continuous AF track priority", and see if that helps.

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    Chris,

    After all the suggestions, have you tried to reproduce the problem and or have any proposed solutions stopped the problem? Let us know.

    Roger

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    Jeff,

    Thanks for the replies, though were you shooting handheld and do recall how long you had the owl sighted and focus bumped in the viewfinder prior to the first release?

    Bill,

    I double checked the manual, and the 5DMII unfortunately does not have that level of Custom Specification.

    Roger,

    I hope to get to it this weekend. Though I am still bit unsure IF there is a true BIF analogue that I can use to practice and benchmark w/o so many of the variables of a BIF.
    Last edited by Chris Korman; 01-27-2011 at 10:37 PM. Reason: clarity

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    moving to photo gear forum
    Chris


    0 .· ` ' / ·. 100
    I have a high sarcasm rate. Deal with it.
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    Well the weather wasn't too good for sunny shots but finally it cleared and I got some in focus shots not the best ones. I think this is the best of them (subject & background wise). I used a tripod and turned off area expansion.

    400mm f/5.6, ISO 2500, 1/3200 sec, F/8, Tripod mounted, AI-Servo AF Central Point, Cropped for Composition, Curves and editing etc.


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