Question regarding focus problems with Canon EF 50mm f/1.4 USM lens

Discussion in 'Canon' started by default, Dec 28, 2006.

  1. default

    default Guest

    At first I thought that my EF 50mm f/1.4 USM lens was not as sharp as my
    50mm f/1.8 II lens but what I have now determined after many photos where
    the focus seems off, is that is is about the same sharpness, but the plane
    of best focus seems to be behind the selected point with the 1.4 (the 1.8
    seems to get it just slightly forward). Pictures of an angled tape measure
    finally prove it. At apertures larger than f/2.8 the 1.4USM back focuses
    enough to be a fairly consistent problem whereas the 1.8 pretty much always
    nails it or focuses just slightly ahead but not enough to matter. I'm using
    the center focus point to check this.

    This is on a Rebel XT (350D). Is this something that would improve with a
    XTi (400D) since the 400D has the higher precision cross sensor on the
    center point for f/2.8 and faster lenses?

    Should the lens be returned to Canon for repair? Is this something they can
    adjust?

    I'm getting kind of annoyed with the 1.4 with it's focus accuracy problem
    and with the fact that it needs about 1/3 stop more shutter time to reach
    the same exposure as the 1.8. Since the 1.4 is only 2/3 stops faster than
    the 1.8, the extra 1/3 stop more shutter time makes the 1.4 only really 1/3
    stops faster than the 1.8. At nearly 5 times the price for another 1/3 stop
    and less accurate focus, I am thinking I should sell the 1.4 and just keep
    the 1.8. Photozone.de seems to think the 1.4 is a better lens than the 1.8
    but I am finding it worse.

    Has anyone else come to this conclusion that the 1.4USM is not worth the
    money at all?
     
    default, Dec 28, 2006
    #1
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  2. default

    Aad Guest

    "default" <> schreef in bericht
    news:pzGkh.530828$5R2.149991@pd7urf3no...
    > At first I thought that my EF 50mm f/1.4 USM lens was not as sharp as my
    > 50mm f/1.8 II lens but what I have now determined after many photos where
    > the focus seems off, is that is is about the same sharpness, but the plane
    > of best focus seems to be behind the selected point with the 1.4 (the 1.8
    > seems to get it just slightly forward). Pictures of an angled tape
    > measure finally prove it. At apertures larger than f/2.8 the 1.4USM back
    > focuses enough to be a fairly consistent problem whereas the 1.8 pretty
    > much always nails it or focuses just slightly ahead but not enough to
    > matter. I'm using the center focus point to check this.
    >
    > This is on a Rebel XT (350D). Is this something that would improve with a
    > XTi (400D) since the 400D has the higher precision cross sensor on the
    > center point for f/2.8 and faster lenses?
    >
    > Should the lens be returned to Canon for repair? Is this something they
    > can adjust?
    >
    > I'm getting kind of annoyed with the 1.4 with it's focus accuracy problem
    > and with the fact that it needs about 1/3 stop more shutter time to reach
    > the same exposure as the 1.8. Since the 1.4 is only 2/3 stops faster than
    > the 1.8, the extra 1/3 stop more shutter time makes the 1.4 only really
    > 1/3 stops faster than the 1.8. At nearly 5 times the price for another
    > 1/3 stop and less accurate focus, I am thinking I should sell the 1.4 and
    > just keep the 1.8. Photozone.de seems to think the 1.4 is a better lens
    > than the 1.8 but I am finding it worse.
    >
    > Has anyone else come to this conclusion that the 1.4USM is not worth the
    > money at all?


    Well, it's better built so it should last longer.
    USM should make it a faster and less noisy lens.
    If thats worth the money? That's up to you.
    It is certanly more difficult to use than the 1.8.
    About the backfocus problem. You shoot return it and get another one.
    (or have yours adjusted)
    kr
    Aad
     
    Aad, Dec 28, 2006
    #2
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  3. default

    default Guest

    "Aad" <> wrote in message
    news:...
    > Well, it's better built so it should last longer.
    > USM should make it a faster and less noisy lens.
    > If thats worth the money? That's up to you.
    > It is certanly more difficult to use than the 1.8.
    > About the backfocus problem. You shoot return it and get another one.
    > (or have yours adjusted)
    > kr
    > Aad


    Thanks for your response. The focusing is much quieter, but not a lot
    faster. The 1.4 overshoots and hunts more than the 1.8 which usually just
    jumps to focus. As for how long it lasts, I could replace the 1.8 many
    times for the price of a 1.4 and I have now read many reports of the focus
    mechanism failing in the 1.4 so it may not really be more reliable. The 1.4
    is wonderful in low light if I can get the focus to be accurate at and below
    f/2.

    It is interesting having both and comparing, but it looks like I'll need to
    send the 1.4 in to Canon to be recalibrated. Hopefully it is something that
    they can do.
     
    default, Dec 28, 2006
    #3
  4. In article <pzGkh.530828$5R2.149991@pd7urf3no> "default" <> writes:
    $ At apertures larger than f/2.8 the 1.4USM back focuses
    $enough to be a fairly consistent problem whereas the 1.8 pretty much always
    $nails it or focuses just slightly ahead but not enough to matter. I'm using
    $the center focus point to check this.

    The aperture at which you shoot has nothing to do with AF; AF is
    always done with the lens wide open.

    Canon's specs say that AF should get you to within DOF (with the
    lens open, since that's how AF is done). Not necessarily exactly on;
    just within DOF. If you're not getting that level of accuracy, then
    yes, your equipment is not functioning correctly.

    $This is on a Rebel XT (350D). Is this something that would improve with a
    $XTi (400D) since the 400D has the higher precision cross sensor on the
    $center point for f/2.8 and faster lenses?

    Maybe; the high-precision sensor is supposed to get to within 1/3 of
    DOF (again, with the lens wide open). Maybe also because AF depends on
    the combination of the body and the lens (you've already seen half of
    this, by getting different results from two lenses on the same body)
    and by switching bodies you may find that both lenses focus correctly,
    or that the 1.4 now works better and the 1.8 works worse. And you
    might get a similar experience by trying a different 350D, too.

    $Should the lens be returned to Canon for repair? Is this something they can
    $adjust?

    Canon can indeed calibrate lenses and/or bodies that are not
    performing within spec.

    See http://www.photo.net/learn/focustest/ for some more info,
    a test procedure, and a whole bunch of comments from people who do
    or don't have focus issues with their cameras.
    --
    Stephen M. Dunn <>
    >>>----------------> http://www.stevedunn.ca/ <----------------<<<

    ------------------------------------------------------------------
    Say hi to my cat -- http://www.stevedunn.ca/photos/toby/
     
    Stephen M. Dunn, Dec 28, 2006
    #4
  5. default

    default Guest

    "Stephen M. Dunn" <> wrote in message
    news:...
    > The aperture at which you shoot has nothing to do with AF; AF is
    > always done with the lens wide open.


    Thanks for your reponse.

    The selected aperture doesn't affect the focus distance that the AF picks,
    but stopping down does increase the depth of field enough that the selected
    focus distance is now within the depth of field which makes the AF good
    enough to use from about f/2.5 and smaller. At f/2.0 the depth of field is
    small enough at close distances for the focus plane to be too far from
    optimal sometimes.


    > Canon's specs say that AF should get you to within DOF (with the
    > lens open, since that's how AF is done). Not necessarily exactly on;
    > just within DOF. If you're not getting that level of accuracy, then
    > yes, your equipment is not functioning correctly.


    It might have a focus distance problem, but it might just be a consistency
    problem. I took another 15 pictures of the tape measure and found that
    sometimes it does get it close enough. It appears that the actual focus
    point might not be exactly under the dot in the viewfinder.

    If I use the AF assist light from a 380EX flash, then the AF seems to be
    more accurate and consistent and it is easy enough to turn off the flash
    before taking the picture. CF4 is set to use the * button for AF so it
    won't refocus when I press the shutter.
     
    default, Dec 28, 2006
    #5
  6. In article <kRXkh.537522$R63.457073@pd7urf1no> "default" <> writes:
    $It might have a focus distance problem, but it might just be a consistency
    $problem. I took another 15 pictures of the tape measure and found that
    $sometimes it does get it close enough. It appears that the actual focus
    $point might not be exactly under the dot in the viewfinder.

    It may not be entirely lined up. Keep in mind, too, that the actual
    AF points are larger than the boxes shown in the viewfinder; I've
    seen claims that they're up to three times the size of the viewfinder
    marking. And anything that's within the sensor's area is fair game.
    That's why the photo.net page on focus testing has nothing but a
    line anywhere near where you put the focus point - to make sure
    that's what the AF system locks onto. Your tape measure, on the
    other hand, has markings both in front of and behind the spot at
    which you're trying to focus, and it's possible that the AF system
    is focusing correctly - just not on the spot where you wanted it
    to.

    A more practical example of how this can be a problem might be a
    portrait. You put the AF point on the subject's eye, but if the
    eyebrow is within the AF point's area of coverage, even though it's
    outside the box in the viewfinder, it's possible that the AF system
    focuses on the eyebrow rather than the eye. You see a misfocused
    picture and think the camera isn't working properly, but in fact it
    is - it's just that the camera's definition of "working properly"
    isn't exactly what you had in mind!
    --
    Stephen M. Dunn <>
    >>>----------------> http://www.stevedunn.ca/ <----------------<<<

    ------------------------------------------------------------------
    Say hi to my cat -- http://www.stevedunn.ca/photos/toby/
     
    Stephen M. Dunn, Dec 29, 2006
    #6
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