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Thread: How to know your ratio using extension tube?

  1. #1
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    Default How to know your ratio using extension tube?

    Anybody know how 2 calculate the ratio if i use extension tubes?

    now i have a 13mm, 21mm, 31mm no autofocus set, & another 25mm kenko autofocus.

    problem is i dunno what magnification if i combine all to use together...

    den the most funny thing i tried is using with a 28-75, totally cannot use... wonder why... with all together, i can still focus with a 75-300 at 75mm range.

    the cam i using is Dynax 7D, so is the 1.5crop a factor for the magnification as well?
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    Moderator ortega's Avatar
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    Take a referance photo of a ruler scale and measure.
    Simple solution to a difficult question.

    Just shoot it!

  3. #3
    Moderator ortega's Avatar
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    Another unit of measure is

    Cool, Way cool and blow me away. ha ha

  4. #4
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    Checkout : http://xoomer.virgilio.it/ripolini/I....htm#Extension



    Quote Originally Posted by Del_CtrlnoAlt
    Anybody know how 2 calculate the ratio if i use extension tubes?

    now i have a 13mm, 21mm, 31mm no autofocus set, & another 25mm kenko autofocus.

    problem is i dunno what magnification if i combine all to use together...

    den the most funny thing i tried is using with a 28-75, totally cannot use... wonder why... with all together, i can still focus with a 75-300 at 75mm range.

    the cam i using is Dynax 7D, so is the 1.5crop a factor for the magnification as well?

  5. #5

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    for non-macro lens,
    if focal length of ext tube = focal length of lens should give 1:1
    meaning if 2x 25mm ext tubes mount with 50mm lens should have 1:1 magnification

    however if focal length of ext tube > focal length of lens, you cannot focus the lens ..
    See my Photo Gallery at the Clubsnap

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    thanks eawtan! but its very very cheem... will try to calculate...

    btw megaweb, whats the diff between using a 50mm lens & 100mm lens & 200mm lens?

    since previously to get 1:1 is for a 35mm, so now with my 1.5x crop, how to factor into the 1:1?
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  7. #7

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    Quote Originally Posted by Del_CtrlnoAlt
    btw megaweb, whats the diff between using a 50mm lens & 100mm lens & 200mm lens?
    I guess there is formula to calcuate the magnification but too chim for me ...

    Different lens have different focusing range. Longer focal length + ext tube can give longer focusing distance. You can see Canon EOS Closeup Lens and Extension Tube Information.


    Quote Originally Posted by Del_CtrlnoAlt
    since previously to get 1:1 is for a 35mm, so now with my 1.5x crop, how to factor into the 1:1?
    should be 1.5:1
    See my Photo Gallery at the Clubsnap

  8. #8
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    not so sure about non-nikon extension tubes, but for nikon ones, the instruction manual that comes with the tube has a table indicating its effect on each nikon lens (magnification ratio). anyone who owns a PK-11A/12/13 can verify?

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