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Thread: Using extension tube with zoom lens for closeup

  1. #1
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    Default Using extension tube with zoom lens for closeup

    I have seen some of you guys use a zoom lens lik 70-200mm lens with a 25mm extension tube for macro work. However I read somewhere that such combi can reach only reach a magnification of 1/8X at 200mm. How is it possible for you guys to have such good magnification? Please enlighten. Thanks.

  2. #2

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    Quote Originally Posted by Celsius
    I have seen some of you guys use a zoom lens lik 70-200mm lens with a 25mm extension tube for macro work. However I read somewhere that such combi can reach only reach a magnification of 1/8X at 200mm. How is it possible for you guys to have such good magnification? Please enlighten. Thanks.
    where did u get the 1/8 figure from? By right at standard focussing distance of 1.5m, a 200mm lense should achieve 200/1500 = 1/7.5 without anything.

  3. #3
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    Quote Originally Posted by xdivider
    where did u get the 1/8 figure from? By right at standard focussing distance of 1.5m, a 200mm lense should achieve 200/1500 = 1/7.5 without anything.
    Magnification = extension tube length / focal length ?
    Or did I get the formula wrong?

  4. #4

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    Quote Originally Posted by Celsius
    Magnification = extension tube length / focal length ?
    Or did I get the formula wrong?
    I think u have to take into consideration the minimum focussing distance of a lens. The lens has a built-in extension.

    If i dun get wrong
    Total extension = tube length + lens extension
    Magnification = Total extension / Focal length of lens

    Assuming the lens has ard 25mm extension by itself, this gives u total 50mm with a tube and ard 50/200 = 1/4 X.

    Correct me if im wrong abt this.

  5. #5
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    You might be right. Still 1/4x seems quite far from life size magnifcation. But judging from some of the closeup/macro shots posted here with such a setup seems quite near 1:1 magnification.

    Quote Originally Posted by xdivider
    I think u have to take into consideration the minimum focussing distance of a lens. The lens has a built-in extension.

    If i dun get wrong
    Total extension = tube length + lens extension
    Magnification = Total extension / Focal length of lens

    Assuming the lens has ard 25mm extension by itself, this gives u total 50mm with a tube and ard 50/200 = 1/4 X.

    Correct me if im wrong abt this.

  6. #6

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    Quote Originally Posted by Celsius
    You might be right. Still 1/4x seems quite far from life size magnifcation. But judging from some of the closeup/macro shots posted here with such a setup seems quite near 1:1 magnification.
    Adding in the crop factor for dslrs, this reaches a respectable 1/3X which is pretty reasonable for large insects like butterflies. Also, some lenses may have close foccusing modes which may affect the calculations.

  7. #7

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    Quote Originally Posted by Celsius
    I have seen some of you guys use a zoom lens lik 70-200mm lens with a 25mm extension tube for macro work. However I read somewhere that such combi can reach only reach a magnification of 1/8X at 200mm. How is it possible for you guys to have such good magnification? Please enlighten. Thanks.
    Hi Celsius,
    I assume you’re referring to my Thread .

    The magnification you gain from Extension tube is dependent on both focal length and extension tube length. For subject below 20cm size, I normally stays at 70mm-100mm focal length, unless I want more working distance then I’ll use 150mm-200mm of course magnification will be lesser.

    Like what xdivider said, crop factor of 1.6X for DLSR plays an important role to increase the magnification as well. But, I always based my calculation using the standard formula we all know. (ExTube length / focal length)

    For my above thread, it was shot at around 100mm, 150mm and 75mm repectively (with 10-20% cropping)

    One of the best way to increase magnification is to use an Extender between the cam and the extension tube. In this matter, the extender will multiply your extension tube strength leaving the minimum focusing distance the same.

    This was shot using 70-200mm + 25mm ext tube + 1.4X TC at 70mm focal length. (cropped about 5% only) Your 25mm now becomes 35mm giving you around 1/2X at 70mm focal length.

    Last edited by Sgt. Pepper; 6th November 2003 at 09:41 AM.

  8. #8

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    Quote Originally Posted by Sgt. Pepper
    Hi Celsius,
    I assume youíre referring to my Thread .

    The magnification you gain from Extension tube is dependent on both focal length and extension tube length. For subject below 20cm size, I normally stays at 70mm-100mm focal length, unless I want more working distance then Iíll use 150mm-200mm of course magnification will be lesser.

    Like what xdivider said, crop factor of 1.6X for DLSR plays an important role to increase the magnification as well. But, I always based my calculation using the standard formula we all know. (ExTube length / focal length)

    For my above thread, it was shot at around 100mm, 150mm and 75mm repectively (with 10-20% cropping)

    One of the best way to increase magnification is to use an Extender between the cam and the extension tube. In this matter, the extender will multiply your extension tube strength leaving the minimum focusing distance the same.

    This was shot using 70-200mm + 25mm ext tube + 1.4X TC at 70mm focal length. (cropped about 5% only) Your 25mm now becomes 35mm giving you around 1/2X at 70mm focal length.

    newbie for this thing

    70-200mm + 25mm ext tube + 1.4X TC

    how close can i get to?

  9. #9

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    Quote Originally Posted by Kelvin^Newbie
    newbie for this thing

    70-200mm + 25mm ext tube + 1.4X TC

    how close can i get to?
    @70mm + 25mm ext tube, the min focusing distance is about 4-5 inches. If you add 1.4X TC, the min focusing distance should not change but the magnification will be higher by 1.4 times.

  10. #10

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    Quote Originally Posted by Sgt. Pepper
    @70mm + 25mm ext tube, the min focusing distance is about 4-5 inches. If you add 1.4X TC, the min focusing distance should not change but the magnification will be higher by 1.4 times.
    i seem so blur wanted to buy and try it out ... how much is 25mm ext tube and 1.4X TC . . .

  11. #11

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    Quote Originally Posted by Kelvin^Newbie
    i seem so blur wanted to buy and try it out ... how much is 25mm ext tube and 1.4X TC . . .
    Kenko extension tube set is going for 280$ +/- (not very sure how much now, but around that price). It comes with 3 sizes: 12mm, 25mm and 36mm.

    Uniplus 25mm is around 90$ at CP.

    1.4X Kenko pro300 is around 320$ @TCW.

    you may call them and check the latest price:
    CP: 63374274
    TCW: 63361956

  12. #12

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    Quote Originally Posted by Sgt. Pepper
    Kenko extension tube ... It comes with 3 sizes: 12mm, 25mm and 36mm.
    The KENKO AUTO EXTENSION TUBE SET contains three tubes of different length, a 12 mm, 20 mm, and 36 mm.
    See my Photo Gallery at the Clubsnap

  13. #13

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    Quote Originally Posted by megaweb
    The KENKO AUTO EXTENSION TUBE SET contains three tubes of different length, a 12 mm, 20 mm, and 36 mm.
    Ooops. sorry, it should be 20mm not 25mm.

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