Extensions for Macro

Discussion in 'Beyond the Basics' started by smoke665, Feb 13, 2018.

  1. Derrel

    Derrel Mr. Rain Cloud

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    A longer lens would benefit much more from extension; the 70 or 77mm lens length would make much more sense to use with an extension tube. I think the 35mm lens length would likely not work very well with extension.


     
  2. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    I've got a 35mm macro and yeah I can't imagine getting much out of it in practical terms with regard to using extension tubes. First up you'd not get much to add before the min and max focus distances move inside the lens itself - ergo making it impossible to use.

    Also moving much closer starts to make lighting and overshadowing of the subject some serious issues. Not impossible, but certainly tricky to work with.

    By all means give them a try, you might get away with 12mm or so before it became nearly impossible.
     
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  3. smoke665

    smoke665 TPF Supporters Supporting Member

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    Okay, my brain starts to overheat when I start getting into crop factors and equivalent focal lengths, but if I have say a 70mm with a magnification factor of .12x on a camera with a crop facto of 1.53 that would give me an eqvalent focal length of (70 x 1,53) 107.1 mm. Does the magnification also increase or remain the same?

    I'm confused on Overead's formula, is this to calculate magnification or focal length?
     
  4. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    ET's don't change the focal length. Nor the 'crop-factor multiplier'. They only change the magnification ratio.

    70mm is 70mm is 70mm is 70mm all day long.
     
  5. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Ignore crop factor.

    Crop factor ONLY applies when you are comparing lenses between different sensor sizes in order to get an idea of the difference. So you don't need to factor it into the calculation; just use the actual focal length of the lens itself. The calculation I posted is to calculate the magnification of the lens

    So for example a 50mm lens with 25mm of tubes would be

    (tube length in mm/focal length) + lenses native magnification = power to :1

    We shall assume native magnification is 0. It won't be, but if its not a macro lens it won't be a typically high value

    (25/50) = 0.5:1 - or half macro.

    If we push the tube length up to 50mm then

    (50/50)+0 = 1:1 (ergo true macro that a macro lens would give)



    Now if we used a 50mm macro lens with 50mm of extension tubing at the lenses closest focus (ergo maximum magnification) we'd get

    (50/50)+1 = 2:1 ergo twice the magnification! (also called twice life size as now the subject is being reflected twice its original size on the lens)
     
  6. smoke665

    smoke665 TPF Supporters Supporting Member

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    @Overread ok that makes more sense. In your first post you had divide the "focal" length by the "extension" .

    Reversing those and using my lens example above 12mm extension/ 70mm focal length = .1714. Add the inherent magnification of .12 and I now have an effective magnification of .2914.

    Using the first math I was coming up with almost 6x. No wonder the brain was overheating.
     
  7. Gary A.

    Gary A. Been spending a lot of time on here!

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    smoke665, it's only $125 ... you blow that on gasoline every other day. Stay home one day and just get the damn tubes. Hands on testing is the best way to figure out what works and what doesn't. I have a garage full of slightly used stuff that doesn't work for me. :cool-98:
     
    Last edited: Feb 20, 2018
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  8. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    oooops - I'll go change that!
     
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  9. smoke665

    smoke665 TPF Supporters Supporting Member

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    Decimal points and The Order Of Operations are the downfall of us all! LOL
     
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  10. Derrel

    Derrel Mr. Rain Cloud

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    Smoke,
    If you want to get into high-magnification macro work, the best course of action is to use a long lens on the camera, and then a reverse-mounted (filter thread-to-filter-thread reversed), short-length lens on the front of the long lens. Something like say a 24mm mounted in-reverse on the front of a 200mm lens.

    Please check out some of the great stuff that comes up on the web and YouTube!

    reverse-mounting a lens on another lens for macro photos - Yahoo Search Results Yahoo Search Results

    Now, as far as extension tubes go: the 12mm and the 20mm lengths (approximate range; may vary by 1 to 5 mm, based on brand! There are 12mm and 13mm and 20,24,and 25mm tubes, in different brands!) are the MOST-useful, so a whole set of three is not a necessity! The 36mm tube that comes in 3-ring sets? That tube has been, in a practical sense, utterly useless to me, for decades. Seriously.

    Another option is to use a 1.4x teleconverter and a telephoto lens, along with a short 12- to 20-mm extension tube; the TC increases magnification, the extension allows close-than-otherwise focusing distances to be used. The Nikkor 300/4 AF-S + TC14e-II has worked well for me in the past in this manner with the Kenko AF tubes.

    Speaking of which....if you have a tele-converter, many people have suggested breaking the glass out of it, and using THAT as a de facto extension tube. I mean...it has the front and rear lens mounts! Perhaps you'd feel more comfortable buying a low-cost, used Pentax AF-capable 2x teleconverter, and removing the glass elements? Maybe use the truck and a block-and-nail to run over it? lol!
     
    Last edited: Feb 20, 2018
  11. petrochemist

    petrochemist TPF junkie!

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    When reversed a 35mm works VERY well with extension.
    Longer lenses need more extension to reach a set magnification, so extension can get very unwieldy with longer lenses. A 300mm lens would need 300mm extension to go from infinity focus to 1:1 with older lenses that move the entire lens to focus that makes the lens around a foot longer for 1:1. Possible with bellows but not practical.

    If the working distance isn't an issue short focal lengths can easily get very high magnifications. IIRC my microfiche lens (~17mm focal length) gave me 4x easily enough.
     
  12. adamhiram

    adamhiram No longer a newbie, moving up!

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    The bottom line with extension tubes is they just allow for a shorter minimum focusing distance. I actually found the lenses that work best to be the opposite of what I would expect. For example, a 35mm that already has a 12" min focusing distance actually benefited quite a bit from extension tubes, provided you are actually able to get extremely close to your subject; I'm not sure the difference would be so dramatic if you can already focus at 6". I found 50mm to be the ideal focal length for extension tubes - with 68mm of extension tubes (all 3 stacked), I can get about 1.5x magnification at a distance of 1.5" - just enough to let in some light. I can get the same with a 35mm lens and 56mm of extension tubes, but am literally 1/8" from the subject, which is not really practical.

    I originally assumed my longer telephoto lenses would be perfect - imagine a 200mm or 300mm lens that could focus just a few inches away - but that just wasn't the case. Besides only giving slightly closer focusing distances on longer lenses, they tended to be too heavy and put a lot of strain on the camera's mount when used with extension tubes.

    The other path many people go is to get a reversing ring, typically used with a 50mm prime with manual aperture ring, along with a bellows which is basically a much longer adjustable extension tube. You can still do this without breaking the bank, but of course it's not nearly as affordable or simple as just adding extension tubes to what you already have. Honestly I would recommend just picking up the Kenko extension tubes to play around with for $124. You'll use them eventually...
     

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