Rebel XT with 550ex Flash and Tamron 18-200mm

Discussion in 'Digital Photography' started by Jamie Dolan, Jul 11, 2006.

  1. Jamie Dolan

    Jamie Dolan Guest

    Hello,

    I have a Rebel XT with a Canon 550ex flash and the Tamron 18-200mm
    lense. I find that the camera is unable to focus with this lense at
    certin focual legneths,, some where around 80 to 150 seem to be the
    most noticable. I am wondering if anyone else have encountered this at
    all, and if there are any known work arounds.


    Thanks,

    jamie
     
    Jamie Dolan, Jul 11, 2006
    #1
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  2. Jamie Dolan

    ColinD Guest

    Jamie Dolan wrote:
    >
    > Hello,
    >
    > I have a Rebel XT with a Canon 550ex flash and the Tamron 18-200mm
    > lense. I find that the camera is unable to focus with this lense at
    > certin focual legneths,, some where around 80 to 150 seem to be the
    > most noticable. I am wondering if anyone else have encountered this at
    > all, and if there are any known work arounds.
    >
    > Thanks,
    >
    > jamie


    You're not going to like this, but the problem is that that lens is
    f/3.5 - f/6.3, and Canon EOS camera autofocus requires f/5.6 minimum
    aperture to be able to focus. As soon as the minimum aperture becomes
    smaller than f/5.6, which happens at some point in the zoom range well
    short of 200mm, the lens will no longer focus.

    This point is not mentioned by the sellers when buying a lens, unless
    you specifically ask. If the lens is new or near new, you may be able
    to get a refund on the grounds that it is not suitable for the purpose
    for which it was bought, depending on the law in your country.

    Colin D.

    --
    Posted via a free Usenet account from http://www.teranews.com
     
    ColinD, Jul 12, 2006
    #2
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  3. Jamie Dolan

    Pete D Guest

    "ColinD" <nospam@127.0.0.1> wrote in message
    news:44B452A1.413AB48A@127.0.0.1...
    >
    >
    > Jamie Dolan wrote:
    >>
    >> Hello,
    >>
    >> I have a Rebel XT with a Canon 550ex flash and the Tamron 18-200mm
    >> lense. I find that the camera is unable to focus with this lense at
    >> certin focual legneths,, some where around 80 to 150 seem to be the
    >> most noticable. I am wondering if anyone else have encountered this at
    >> all, and if there are any known work arounds.
    >>
    >> Thanks,
    >>
    >> jamie

    >
    > You're not going to like this, but the problem is that that lens is
    > f/3.5 - f/6.3, and Canon EOS camera autofocus requires f/5.6 minimum
    > aperture to be able to focus. As soon as the minimum aperture becomes
    > smaller than f/5.6, which happens at some point in the zoom range well
    > short of 200mm, the lens will no longer focus.
    >
    > This point is not mentioned by the sellers when buying a lens, unless
    > you specifically ask. If the lens is new or near new, you may be able
    > to get a refund on the grounds that it is not suitable for the purpose
    > for which it was bought, depending on the law in your country.
    >
    > Colin D.
    >


    Now that is skanky, I guess it is also a factor to watch ot for when you are
    looking for a lens with such a wide range. Happy I bought the 70-300mm DG
    APO F4.0-5.6, still have AF with a 1.4 converter.:)
     
    Pete D, Jul 12, 2006
    #3
  4. Jamie Dolan

    Jamie Dolan Guest

    HI,

    Thank you so much for telling me what is going on. I have been just
    puzzled, and the people at the camera store I got it from didnt know at
    all either.

    I do have another flash question.. I will write a new post about it.

    Thanks again.

    Jamie

    ColinD wrote:
    > Jamie Dolan wrote:
    > >
    > > Hello,
    > >
    > > I have a Rebel XT with a Canon 550ex flash and the Tamron 18-200mm
    > > lense. I find that the camera is unable to focus with this lense at
    > > certin focual legneths,, some where around 80 to 150 seem to be the
    > > most noticable. I am wondering if anyone else have encountered this at
    > > all, and if there are any known work arounds.
    > >
    > > Thanks,
    > >
    > > jamie

    >
    > You're not going to like this, but the problem is that that lens is
    > f/3.5 - f/6.3, and Canon EOS camera autofocus requires f/5.6 minimum
    > aperture to be able to focus. As soon as the minimum aperture becomes
    > smaller than f/5.6, which happens at some point in the zoom range well
    > short of 200mm, the lens will no longer focus.
    >
    > This point is not mentioned by the sellers when buying a lens, unless
    > you specifically ask. If the lens is new or near new, you may be able
    > to get a refund on the grounds that it is not suitable for the purpose
    > for which it was bought, depending on the law in your country.
    >
    > Colin D.
    >
    > --
    > Posted via a free Usenet account from http://www.teranews.com
     
    Jamie Dolan, Jul 12, 2006
    #4
  5. Jamie Dolan

    Jamie Dolan Guest


    > You're not going to like this, but the problem is that that lens is
    > f/3.5 - f/6.3, and Canon EOS camera autofocus requires f/5.6 minimum
    > aperture to be able to focus. As soon as the minimum aperture becomes


    Is this specfic to a flash use situation or a low light situation possiable?
    Because the lense does auto focus in day light at much lower f stops, i.e.
    f/11

    thanks

    -jamie

    > smaller than f/5.6, which happens at some point in the zoom range well
    > short of 200mm, the lens will no longer focus.
    >
    > This point is not mentioned by the sellers when buying a lens, unless
    > you specifically ask. If the lens is new or near new, you may be able
    > to get a refund on the grounds that it is not suitable for the purpose
    > for which it was bought, depending on the law in your country.
    >
    > Colin D.
    >
    > --
    > Posted via a free Usenet account from http://www.teranews.com
    >
     
    Jamie Dolan, Jul 12, 2006
    #5
  6. Jamie Dolan

    ColinD Guest

    Jamie Dolan wrote:
    >
    > > You're not going to like this, but the problem is that that lens is
    > > f/3.5 - f/6.3, and Canon EOS camera autofocus requires f/5.6 minimum
    > > aperture to be able to focus. As soon as the minimum aperture becomes

    >
    > Is this specfic to a flash use situation or a low light situation possiable?
    > Because the lense does auto focus in day light at much lower f stops, i.e.
    > f/11
    >
    > thanks
    >
    > -jamie


    Jamie, top posting makes it awkward when replying to a thread like this,
    because the messages are out of order. However, to your question.
    The camera always focuses with the lens at full aperture, even though
    you may actually take the shot at f/11. Whether you let the camera
    decide what stop and shutter speed to use, by selecting the green box or
    'P' (Program) setting, or whether you set the mode to Av (aperture
    priority) where you can select the aperture and let the camera select
    the shutter speed, the camera will focus wide open and then stop down
    for the exposure.

    The lens may autofocus at f/6.3, if the scene is of sufficient contrast,
    but it's not reliable, and it's outside Canon's specs for the EOS
    system.

    With flash, the camera will focus and shoot wide open, to make maximum
    use of the light *unless* you shoot in Av mode, when the camera will
    shoot at the selected aperture, But in this case the camera will meter
    the scene and expose for the ambient light, and use the flash as a fill
    flash. This means that in a dim or night situation, the shutter may
    well expose for whole seconds, and you are left with a badly shaken
    image from the long exposure.
    >

    Colin D.

    --
    Posted via a free Usenet account from http://www.teranews.com
     
    ColinD, Jul 13, 2006
    #6
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