Using AF points

Discussion in 'Digital Photography' started by fishfry, Feb 9, 2006.

  1. fishfry

    fishfry Guest

    I have a Digital Rebel 350XT with 7 autofocus points. It does the right
    thing in obvious situations, but gets hopelessly confused when shooting,
    for example, a scenic shot with tree branches in the foreground. Slight
    variations in composition cause it to change its mind about what to
    focus on.

    It seems to make more sense to just tell it to use only the center AF
    point. Then focus-lock on whatever you want to focus on, recompose, and
    shoot.

    Can anyone explain the advantage of having it use all the AF points?
     
    fishfry, Feb 9, 2006
    #1
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  2. > I have a Digital Rebel 350XT with 7 autofocus points. It does the right
    > thing in obvious situations, but gets hopelessly confused when shooting,
    > for example, a scenic shot with tree branches in the foreground. Slight
    > variations in composition cause it to change its mind about what to
    > focus on.
    >
    > It seems to make more sense to just tell it to use only the center AF
    > point. Then focus-lock on whatever you want to focus on, recompose, and
    > shoot.


    Agreed. I hardly ever use the full auto focus mode for the exact reasons
    you state. In a simple scene the centre point, plus optional
    recomposing, works fine. In complex scenes the auto system just gets
    confused and forces me to shoot using the centre point anyway. So my 20D
    stays with the centre point selected almost all the time.

    > Can anyone explain the advantage of having it use all the AF points?


    It can be useful when your subjects are moving and you don't have time
    to recompose the shot, but it can still be fooled. Have a look at this
    remarkable shot a friend of mine took:

    http://www.esses.co.uk/tmp/wasp.jpg

    An Aston Martin racer barrelling towards him at nearly 200mph, and the
    camera finds a wasp to focus on. :eek:)

    The auto focus technology is great, but whether it is really that useful
    in a "serious" camera is more debatable.
     
    Derek Fountain, Feb 9, 2006
    #2
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  3. "Derek Fountain" <> wrote in message
    news:43eafec6$0$36849$...
    >
    > It can be useful when your subjects are moving and you don't have time
    > to recompose the shot, but it can still be fooled. Have a look at this
    > remarkable shot a friend of mine took:
    >
    > http://www.esses.co.uk/tmp/wasp.jpg
    >
    > An Aston Martin racer barrelling towards him at nearly 200mph, and the
    > camera finds a wasp to focus on. :eek:)


    Interesting shot - assuming that the EXIF info hasn't been doctored and is
    merely truncated, it was taken by a 10D, at the full resolution of 3072 x
    2048 pixels. My 10D certainly doesn't have AF points that far from the
    centre of the field.

    --
    M Stewart
    Milton Keynes, UK
     
    Malcolm Stewart, Feb 9, 2006
    #3
  4. fishfry

    John Fryatt Guest

    fishfry wrote:
    > I have a Digital Rebel 350XT with 7 autofocus points. It does the right
    > thing in obvious situations, but gets hopelessly confused when shooting,
    > for example, a scenic shot with tree branches in the foreground. Slight
    > variations in composition cause it to change its mind about what to
    > focus on.
    >
    > It seems to make more sense to just tell it to use only the center AF
    > point. Then focus-lock on whatever you want to focus on, recompose, and
    > shoot.


    That's what I do. Seems more under my control than using multiple AF points.

    > Can anyone explain the advantage of having it use all the AF points?


    I'd be interested to hear opinions on this as well. Maybe it's just a
    marketing thing that not many use in practice.

    John
     
    John Fryatt, Feb 9, 2006
    #4
  5. John Fryatt <> wrote:

    : I'd be interested to hear opinions on this as well. Maybe it's just a
    : marketing thing that not many use in practice.

    For those users or situations where full auto is useful or needed, having
    some form of auto that takes all the photo training out of the process can
    be good. Notice I also mentioned situations such as when conditions may
    change very rapidly. But for most situations where at least minimal
    composition and thought is possible, less auto is good. Having various
    degrees of auto from "don't think" to "did you bring your scientific
    calculator" is good. IMHO

    Randy

    ==========
    Randy Berbaum
    Champaign, IL
     
    Randy Berbaum, Feb 9, 2006
    #5
  6. fishfry

    Tesco News Guest

    "fishfry" <> wrote in message
    news:...
    >I have a Digital Rebel 350XT with 7 autofocus points. It does the right
    > thing in obvious situations, but gets hopelessly confused when shooting,
    > for example, a scenic shot with tree branches in the foreground. Slight
    > variations in composition cause it to change its mind about what to
    > focus on.
    >
    > It seems to make more sense to just tell it to use only the center AF
    > point. Then focus-lock on whatever you want to focus on, recompose, and
    > shoot.
    >
    > Can anyone explain the advantage of having it use all the AF points?


    Hi.

    I believe there is some way that the Camera will set the aperture and the
    focus, so that the furthest and nearest Focus Points wlll be withing the
    Depth of Field. Assuming the lighting and ISO settings give it sufficient
    depth.

    How useful is that function?

    About as good as the Nikon D70. When all Focus Points are activated, it
    will focus on the closest one.

    Roy G
     
    Tesco News, Feb 9, 2006
    #6
  7. fishfry

    Steve Wolfe Guest

    >I have a Digital Rebel 350XT with 7 autofocus points. It does the right
    > thing in obvious situations, but gets hopelessly confused when shooting,
    > for example, a scenic shot with tree branches in the foreground. Slight
    > variations in composition cause it to change its mind about what to
    > focus on.
    >
    > It seems to make more sense to just tell it to use only the center AF
    > point. Then focus-lock on whatever you want to focus on, recompose, and
    > shoot.
    >
    > Can anyone explain the advantage of having it use all the AF points?


    If you're in AI-Servo, some of Canon's cameras can track a moving object
    across the field of view, transferring from one AF point to another. I'm
    not sure if the 350D can do that, or just the higher-end models.

    steve
     
    Steve Wolfe, Feb 9, 2006
    #7
  8. In article <>,
    fishfry <> wrote:

    > Can anyone explain the advantage of having it use all the AF points?


    Great if you like our-of-focus pictures. Turn off all points except for
    one.
     
    Randall Ainsworth, Feb 9, 2006
    #8
  9. fishfry

    Bill Funk Guest

    On Thu, 09 Feb 2006 08:34:07 +0000, Derek Fountain
    <> wrote:

    >> I have a Digital Rebel 350XT with 7 autofocus points. It does the right
    >> thing in obvious situations, but gets hopelessly confused when shooting,
    >> for example, a scenic shot with tree branches in the foreground. Slight
    >> variations in composition cause it to change its mind about what to
    >> focus on.
    >>
    >> It seems to make more sense to just tell it to use only the center AF
    >> point. Then focus-lock on whatever you want to focus on, recompose, and
    >> shoot.

    >
    >Agreed. I hardly ever use the full auto focus mode for the exact reasons
    >you state. In a simple scene the centre point, plus optional
    >recomposing, works fine. In complex scenes the auto system just gets
    >confused and forces me to shoot using the centre point anyway. So my 20D
    >stays with the centre point selected almost all the time.
    >
    >> Can anyone explain the advantage of having it use all the AF points?

    >
    >It can be useful when your subjects are moving and you don't have time
    >to recompose the shot, but it can still be fooled. Have a look at this
    >remarkable shot a friend of mine took:
    >
    >http://www.esses.co.uk/tmp/wasp.jpg
    >
    >An Aston Martin racer barrelling towards him at nearly 200mph, and the
    >camera finds a wasp to focus on. :eek:)
    >
    >The auto focus technology is great, but whether it is really that useful
    >in a "serious" camera is more debatable.


    Interesting.
    *Everything* but the wasp is equally blurred, inculding the track
    nearest the wasp, and the camera doesn't have a focus point where the
    wasp is. Is the shot cropped? No, it doesn't appear so; the URL of the
    pic (http://www.esses.co.uk/tmp/wasp.jpg) shows the size of the
    original is 3072x2048.
    So, how was this really done?

    --
    Bill Funk
    replace "g" with "a"
     
    Bill Funk, Feb 9, 2006
    #9
  10. fishfry

    Bill Funk Guest

    On Thu, 09 Feb 2006 10:59:51 GMT, "Tesco News"
    <> wrote:

    >"fishfry" <> wrote in message
    >news:...
    >>I have a Digital Rebel 350XT with 7 autofocus points. It does the right
    >> thing in obvious situations, but gets hopelessly confused when shooting,
    >> for example, a scenic shot with tree branches in the foreground. Slight
    >> variations in composition cause it to change its mind about what to
    >> focus on.
    >>
    >> It seems to make more sense to just tell it to use only the center AF
    >> point. Then focus-lock on whatever you want to focus on, recompose, and
    >> shoot.
    >>
    >> Can anyone explain the advantage of having it use all the AF points?

    >
    >Hi.
    >
    >I believe there is some way that the Camera will set the aperture and the
    >focus, so that the furthest and nearest Focus Points wlll be withing the
    >Depth of Field. Assuming the lighting and ISO settings give it sufficient
    >depth.


    Yes, A-DEP, or Auto DEPth of field.
    >
    >How useful is that function?


    It can be very useful. For groups of people where what's wanted is
    everyone in focus, for example, it can work well.
    >
    >About as good as the Nikon D70. When all Focus Points are activated, it
    >will focus on the closest one.
    >
    >Roy G
    >


    --
    Bill Funk
    replace "g" with "a"
     
    Bill Funk, Feb 9, 2006
    #10
  11. fishfry

    Guest

    Tesco News wrote:
    > I believe there is some way that the Camera will set the aperture and the
    > focus, so that the furthest and nearest Focus Points wlll be withing the
    > Depth of Field. Assuming the lighting and ISO settings give it sufficient
    > depth.
    >
    > How useful is that function?


    Yes, the DEP/ADEP mode may be useful for some particular images... I
    find it actually more practical than using the DoF preview button,
    which often makes the viewfinder too dark to properly estimate blur
    (anyway you can use both).


    Otherwise, I'll answer as everybody here to the initial question : it's
    much more practical to have only one AF target enabled (usually the one
    in the center) to focus and then recompose, than to have the automatic
    AF selector catching anything in sight (ie everything you don't want).


    Btw, I wonder also why Canon didn't keep on with the Eye Control
    (available on EOS50e, which may translate into ElanE or Elan2E for US)?

    It might have been a good idea in theory (especially with the present
    problem), but tricky to get to work properly in practice? Any user's
    opinions?

    "The difference between theory and practice is generally greater in
    practice than in theory"
    Nicolas
     
    , Feb 9, 2006
    #11
  12. > Interesting.
    > *Everything* but the wasp is equally blurred, inculding the track
    > nearest the wasp, and the camera doesn't have a focus point where the
    > wasp is. Is the shot cropped? No, it doesn't appear so; the URL of the
    > pic (http://www.esses.co.uk/tmp/wasp.jpg) shows the size of the
    > original is 3072x2048.
    > So, how was this really done?


    He maintains that that is the image that came from the camera, given a
    small amount of levels correction in Photoshop. I have no reason to
    disbelieve him - he's normally totally honest about his images.

    He said it was the second shot from a burst, so if the camera focused on
    the wasp for the first shot, then didn't refocus for the second shot,
    that would explain how the wasp is in focus but not on one of the AF
    points. However, he also thinks he was in AF servo mode, since the cars
    were coming towards him. Which kind of blows that idea out of the water.

    Dunno. Nor does he. As you say, "interesting". :eek:)
     
    Derek Fountain, Feb 9, 2006
    #12
  13. fishfry

    Guest

    fishfry wrote:
    > Can anyone explain the advantage of having it use all the AF points?


    After a bit of digging, I found the beginning of an answer in
    http://visual-vacations.com/Photography/focus-recompose_sucks.htm .

    It seems to me that this argument applies more to situations with very
    narrow DoF, like shooting with your brand new Cakon 600mm f/1.2 L VR DO
    EX HSM *_at full aperture_*. Well, I may be exaggerating a bit, I'll be
    careful with a 50/1.8 in low light.
     
    , Feb 9, 2006
    #13
  14. fishfry

    Paul J Gans Guest

    fishfry <> wrote:
    >I have a Digital Rebel 350XT with 7 autofocus points. It does the right
    >thing in obvious situations, but gets hopelessly confused when shooting,
    >for example, a scenic shot with tree branches in the foreground. Slight
    >variations in composition cause it to change its mind about what to
    >focus on.


    >It seems to make more sense to just tell it to use only the center AF
    >point. Then focus-lock on whatever you want to focus on, recompose, and
    >shoot.


    >Can anyone explain the advantage of having it use all the AF points?


    No. Never figured that out. I did the same thing you did and
    just set it (it being a 300D in my case) to the center spot and
    left it there.

    ----- Paul J. Gans
     
    Paul J Gans, Feb 9, 2006
    #14
  15. fishfry

    Paul J Gans Guest

    Derek Fountain <> wrote:
    >> I have a Digital Rebel 350XT with 7 autofocus points. It does the right
    >> thing in obvious situations, but gets hopelessly confused when shooting,
    >> for example, a scenic shot with tree branches in the foreground. Slight
    >> variations in composition cause it to change its mind about what to
    >> focus on.
    >>
    >> It seems to make more sense to just tell it to use only the center AF
    >> point. Then focus-lock on whatever you want to focus on, recompose, and
    >> shoot.


    >Agreed. I hardly ever use the full auto focus mode for the exact reasons
    >you state. In a simple scene the centre point, plus optional
    >recomposing, works fine. In complex scenes the auto system just gets
    >confused and forces me to shoot using the centre point anyway. So my 20D
    >stays with the centre point selected almost all the time.


    >> Can anyone explain the advantage of having it use all the AF points?


    >It can be useful when your subjects are moving and you don't have time
    >to recompose the shot, but it can still be fooled. Have a look at this
    >remarkable shot a friend of mine took:


    >http://www.esses.co.uk/tmp/wasp.jpg


    >An Aston Martin racer barrelling towards him at nearly 200mph, and the
    >camera finds a wasp to focus on. :eek:)


    >The auto focus technology is great, but whether it is really that useful
    >in a "serious" camera is more debatable.


    Agreed. A single focus spot with perhaps setting to allow
    for a choice of region to use for exposure setting.

    Should be cheaper to produce too.

    Sometimes gimcracks are just that.

    ---- Paul J. Gans
     
    Paul J Gans, Feb 9, 2006
    #15
  16. fishfry

    Eatmorepies Guest

    "fishfry" <> wrote in message
    news:...
    >I have a Digital Rebel 350XT with 7 autofocus points. It does the right
    > thing in obvious situations, but gets hopelessly confused when shooting,
    > for example, a scenic shot with tree branches in the foreground. Slight
    > variations in composition cause it to change its mind about what to
    > focus on.
    >
    > It seems to make more sense to just tell it to use only the center AF
    > point. Then focus-lock on whatever you want to focus on, recompose, and
    > shoot.
    >
    > Can anyone explain the advantage of having it use all the AF points?


    DEP mode.

    A like the various focus points even though I usually set the camera on the
    centre one. Sometines I use the camera in portrait mode and want to sit my
    subject in the upper or lower part of the frame - and use servo focus. Thus
    I select my focus spot.

    John
     
    Eatmorepies, Feb 9, 2006
    #16
  17. fishfry

    secheese Guest

    On Wed, 08 Feb 2006 23:56:59 -0800, fishfry <>
    wrote:

    >It seems to make more sense to just tell it to use only the center AF
    >point. Then focus-lock on whatever you want to focus on, recompose, and
    >shoot.


    Precisely what good photographers do.

    >Can anyone explain the advantage of having it use all the AF points?


    Yep... for Joe Average that wants to point-and-shoot.

    Most digicams these days, have way to many "auto" features. If you
    wanna take a snapshot, go auto... if you wanna make a photograph,
    learn to use ALL the functionality of your camera; especially its
    manual modes.
     
    secheese, Feb 10, 2006
    #17
  18. fishfry

    Paul J Gans Guest

    secheese <> wrote:
    >On Wed, 08 Feb 2006 23:56:59 -0800, fishfry <>
    >wrote:


    >>It seems to make more sense to just tell it to use only the center AF
    >>point. Then focus-lock on whatever you want to focus on, recompose, and
    >>shoot.


    >Precisely what good photographers do.


    >>Can anyone explain the advantage of having it use all the AF points?


    >Yep... for Joe Average that wants to point-and-shoot.


    >Most digicams these days, have way to many "auto" features. If you
    >wanna take a snapshot, go auto... if you wanna make a photograph,
    >learn to use ALL the functionality of your camera; especially its
    >manual modes.


    I think you might have missed the point. With all AF points
    active, Joe Average isn't going to get a good shot. He'll
    end up focussed on whatever is closer and on an AF point such
    as a fence post, a tree branch, or whatever.

    ----- Paul J. Gans
     
    Paul J Gans, Feb 10, 2006
    #18
  19. John Fryatt wrote:
    > fishfry wrote:
    >
    >> I have a Digital Rebel 350XT with 7 autofocus points. It does the
    >> right thing in obvious situations, but gets hopelessly confused when
    >> shooting, for example, a scenic shot with tree branches in the
    >> foreground. Slight variations in composition cause it to change its
    >> mind about what to focus on.
    >>
    >> It seems to make more sense to just tell it to use only the center AF
    >> point. Then focus-lock on whatever you want to focus on, recompose,
    >> and shoot.

    >
    > That's what I do. Seems more under my control than using multiple AF
    > points.
    >
    >> Can anyone explain the advantage of having it use all the AF points?

    >
    > I'd be interested to hear opinions on this as well. Maybe it's just a
    > marketing thing that not many use in practice.


    On general photographs with no depth of field issues, multiple
    points can all feed the focus algorithm, and the highest contrast
    points get selected which can provide a more precise focus.

    It is not necessarily a near versus far issue, as contrast
    is also important in what focus point gets chosen.

    Multiple focus points, in my opinion, are great for choosing
    what part of the subject you want in focus, WITHOUT having
    to recompose. This is very important for following action,
    where there is no time to center focus and recompose.
    So don't simply select the center focus point. Select the
    point that gives the the best composition with the subject
    that must be in focus. For wildlife, that is almost always
    the eyes.

    Examples: Following a bird in flight with a clear blue sky:
    use all focus points and let the camera find the bird and
    focus on it. Exception: the bird fills the field and you
    want focus on the birds eye, then choose one focus point.
    But if there is any detail in the background, AF systems get
    confused, so one focus point on the subject is best.

    General: use one focus point and move the focus point around
    so as to keep the focus point on the eye of the subject.
    This is easier to do on more advanced cameras like a 1D Mark II
    with 45 AF points.

    Examples, for each image note where the eye is, and in most
    cases a focus point is on the eye:
    Birds:
    http://www.clarkvision.com/galleries/gallery.bird
    Bears:
    http://www.clarkvision.com/galleries/gallery.bear

    Roger
     
    Roger N. Clark (change username to rnclark), Feb 13, 2006
    #19
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