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Thread: Question on AF points

  1. #1

    Default Question on AF points

    Hi all,

    My camera has 9 AF points and I believe some other cameras have more. However, I cannot appreciate the multiple AF points as most of the time the camera give me focus at the wrong places.

    So end up, I set the camera such that it always use the 'centre' AF point and I will use that centre AF point to focus and then re-compose my picture.

    Am I silly for not being able to appreciate the multiple AF points?

    Your views please.

    Thanks.

  2. #2

    Default Re: Question on AF points

    When you said focus on the wrong places, do you mean you allow the camera to select the AF point, or you specify the AF point but still the focus is off in that area?

  3. #3

    Default Re: Question on AF points

    Quote Originally Posted by ahbian View Post
    When you said focus on the wrong places, do you mean you allow the camera to select the AF point, or you specify the AF point but still the focus is off in that area?
    Yes, I meant I allow the camera to auto select the AF point(s). And apparently I couldn't appreciate such auto feature, so nowadays, I always select the 'centre' one, focus, and then recompose.

  4. #4

    Default Re: Question on AF points

    Quote Originally Posted by ilovesoftpawn View Post
    Yes, I meant I allow the camera to auto select the AF point(s). And apparently I couldn't appreciate such auto feature, so nowadays, I always select the 'centre' one, focus, and then recompose.
    If you let the camera select, then there is less control on your part. It might tend to grab areas of "high contrast etc" which might not be your intended subject of focus.

    Choosing your own AF allows you more control, using centre AF and recompose usually works if your DOF is not too little.

    My preference is to compose your picture first, then choose the (off centre) AF that covers your intended subject. Look at the section under Manual AF point selection in the link below, the photo is what I meant.

    http://www.usa.canon.com/dlc/control...articleID=3049

    This is one of the reasons why people like more AF points, sometimes it not for the purpose of using them all together in a single shot.
    Last edited by ahbian; 6th July 2010 at 12:14 PM.

  5. #5

    Default Re: Question on AF points

    Quote Originally Posted by ahbian View Post
    If you let the camera select, then there is less control on your part. It might tend to grab areas of "high contrast etc" which might not be your intended subject of focus.

    Choosing your own AF allows you more control, using centre AF and recompose usually works if your DOF is not too little.

    My preference is to compose your picture first, then choose the (off centre) AF that covers your intended subject. Look at the section under Manual AF point selection in the link below, the photo is what I meant.

    http://www.usa.canon.com/dlc/control...articleID=3049

    This is one of the reasons why people like more AF points, sometimes it not for the purpose of using them all together in a single shot.
    Thanks. The link is useful.

    Your method of composing the picture first and then manually choose the AF points is slightly different from my 'usual' way of shooting but it's nonetheless a viable suggestion. I will give it a try and I think I need to exercise my thumb more and make it move quicker.

  6. #6
    Senior Member sinned79's Avatar
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    Default Re: Question on AF points

    Quote Originally Posted by ilovesoftpawn View Post
    Hi all,

    My camera has 9 AF points and I believe some other cameras have more. However, I cannot appreciate the multiple AF points as most of the time the camera give me focus at the wrong places.

    So end up, I set the camera such that it always use the 'centre' AF point and I will use that centre AF point to focus and then re-compose my picture.

    Am I silly for not being able to appreciate the multiple AF points?

    Your views please.

    Thanks.
    u are not alone

    this is what i had been doing.

    there is a problem with 5DMKII... only the center focusing is fast... so i usually only use center focusing.

  7. #7

    Default Re: Question on AF points

    Using the centre AF point to focus and recompose, subject will always be in front of focal plane.

  8. #8

    Default Re: Question on AF points

    Quote Originally Posted by sinned79 View Post
    u are not alone

    this is what i had been doing.

    there is a problem with 5DMKII... only the center focusing is fast... so i usually only use center focusing.
    Phew. Glad to know that I am not alone.

  9. #9

    Default Re: Question on AF points

    Quote Originally Posted by sinned79 View Post
    u are not alone

    this is what i had been doing.

    there is a problem with 5DMKII... only the center focusing is fast... so i usually only use center focusing.
    Quote Originally Posted by GRbenji View Post
    Using the centre AF point to focus and recompose, subject will always be in front of focal plane.
    Thanks. I thought so too.

  10. #10
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    Default Re: Question on AF points

    Quote Originally Posted by GRbenji View Post
    Using the centre AF point to focus and recompose, subject will always be in front of focal plane.
    I don't think so but I am not sure. Can you elaborate?
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  11. #11

    Default Re: Question on AF points

    Quote Originally Posted by GRbenji View Post
    Using the centre AF point to focus and recompose, subject will always be in front of focal plane.
    If u r using a shallow dof (like 85mm f1.4), and u use center af to focus on eyes and recompose, ur subject's eyes will definitely be oof.

  12. #12

    Default Re: Question on AF points

    Quote Originally Posted by torak View Post
    If u r using a shallow dof (like 85mm f1.4), and u use center af to focus on eyes and recompose, ur subject's eyes will definitely be oof.
    Isn't that similar to what I've said? In front or behind focal plane means not in perfect focus. DOF affect how much it is oof.

  13. #13

    Default Re: Question on AF points

    Quote Originally Posted by LBL2009 View Post
    I don't think so but I am not sure. Can you elaborate?
    Read this.

    However, the effect is minimal.
    Last edited by GRbenji; 6th July 2010 at 04:30 PM.

  14. #14
    Senior Member ovaltinemilo's Avatar
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    Default Re: Question on AF points

    Quote Originally Posted by ilovesoftpawn View Post
    Hi all,

    My camera has 9 AF points and I believe some other cameras have more. However, I cannot appreciate the multiple AF points as most of the time the camera give me focus at the wrong places.

    So end up, I set the camera such that it always use the 'centre' AF point and I will use that centre AF point to focus and then re-compose my picture.

    Am I silly for not being able to appreciate the multiple AF points?

    Your views please.

    Thanks.
    I think it's better to choose your own Af point. Most ppl use the centre AF point then recompose.

    If you are using a lens that give very thin DOF, you will come to realise the usefulness when the usual center af + recompose will most prob give oof.
    ...:::..::.Nikon.::.:::..
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  15. #15

    Default Re: Question on AF points

    Quote Originally Posted by GRbenji View Post
    Read this.

    However, the effect is minimal.
    Thanks for sharing, quite a heavy read.

    Still haven't gotten my head around how the numbers would work out for a lens with a much closer focusing distance. Less impact than the 10-22mm?

    I do think most of the time the technique of centre AF and recompose would give acceptable results, if not can fine tune by selecting AF points. For me, the scrolling through of AF points is quite instinctive already.

  16. #16
    Senior Member Numnumball's Avatar
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    Default Re: Question on AF points

    Quote Originally Posted by torak View Post
    If u r using a shallow dof (like 85mm f1.4), and u use center af to focus on eyes and recompose, ur subject's eyes will definitely be oof.
    D700/85f1.4 user here.. I choose muliple af points and focus at hyperfocal distance (norm a point in between both eyes), no prob.. Mayb u can try n do the same.

    of cos other factors like position of ur subject parallel to ur focal plane will mote or less eliminate the above prob..
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  17. #17

    Default Re: Question on AF points

    depends what you do.

    for sports, i select my AF points manually. some cameras when you use the centre AF point will suddenly become more quicker.
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  18. #18

    Default Re: Question on AF points

    from wat i've read, the focusing and recomposing generally works fine - its not very noticeable unless in extreme conditions, like mentioned above, such as very shallow DOF. however, if i can use an AF point that is suited to my composition, i generally manually select it, to avoid any chance of getting a slightly out of focus image.. if not, i focus and recompose
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  19. #19

    Default Re: Question on AF points

    I also having the same problem.

    1. Center is fast but when you are shooting portraits, face of the subject may be OOF if DPF is swallow (torso sharp but not face).
    2. Manually adjust AF point can be slow (lag by >3 sec). By the time you select your previous desirable AF point, the subject has long shifted his/her position. Definitely not recommended for SPORTS.

    I'm a Canon user as you can see. Is Nikkon matrix AF system works better? Like to listen to some of the 1D, 7D and Nikkon users comment.

  20. #20
    Moderator Octarine's Avatar
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    Default Re: Question on AF points

    Quote Originally Posted by kineticworks View Post
    2. Manually adjust AF point can be slow (lag by >3 sec). By the time you select your previous desirable AF point, the subject has long shifted his/her position. Definitely not recommended for SPORTS.
    I use one CFn where you can put the AF point selection at the arrow keys, center button is center AF point. Works pretty well and is faster than 3s, not even looking when used to it.
    I'm a Canon user as you can see. Is Nikkon matrix AF system works better? Like to listen to some of the 1D, 7D and Nikkon users comment.
    Are you sure this exists? Matrix Metering system is also used in Canon bodies, they just name it differently.
    Last edited by Octarine; 8th July 2010 at 11:38 PM.
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