Canon 70-200mm F2.8 With 1.4 Extender

Discussion in 'Digital Photography' started by Russell, May 8, 2005.

  1. Russell

    Russell Guest

    According to Canon's instructions:

    "If an extender (optional) is attached and the maximum aperture of the lens
    is f/5.6 or smaller, AF will not be possible. For details, see the
    Extender's instructions."

    Does that mean you loose Auto Focus when using a Canon 70-200mm F2.8 with
    1.4 Extender? Or does AF work, but only from F8 and smaller (F5.6, plus the
    1 stop loss from the converter).

    Anyone know why this is?
    Russell, May 8, 2005
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  2. Russell

    C Wright Guest

    You are trying to make it too complicated! The lens always focuses at
    maximum aperture, then stops down when the shutter button is pressed. So
    the only thing that you need to be concerned about is the maximum aperture
    available. The 1.4 extender will cost you one stop so your f2.8 lens will,
    in effect, become an f4 lens. That is enough aperture for auto focus to
    always work.
    C Wright, May 8, 2005
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  3. Russell

    [BnH] Guest

    [BnH], May 8, 2005
  4. Russell

    Bill Hilton Guest

    "If an extender (optional) is attached and the maximum aperture of the
    This is true for the consumer cameras, but with the Pro models like the
    1Ds and 1D series it's f/8.
    No, because the "max aperture" is f/4 with this combo. You can also
    use the 2x and the max aperture is f/5.6. It means you can't put the
    1.4x on an f/5.6 lens and AF or the 2x on an f/4 lens and AF, that's
    It will AF with the lens wide open and then stop down to the desired
    aperture when you actually take the shot. So you can set it for f/32
    but with the 1.4x or 2x t/c on the f/2.8 lens it will still AF, because
    focussing takes place while the lens is wide open.
    Because the body needs a certain amount of light and contrast to
    autofocus reliably.

    Bill Hilton, May 8, 2005
  5. Russell

    Marius Guest

    Marius, May 8, 2005
  6. Russell

    Russell Guest

    Cheers all.
    Russell, May 8, 2005

  7. Ding, ding , ding! Finally the correct answer.
    Dave R knows who, May 9, 2005
  8. Russell

    JPS Guest

    In message <427e611f$0$803$>,
    Of course, AF can become very slow and very inaccurate when forced to
    work with a TC.
    JPS, May 13, 2005
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