[test] extension tubes on magnification of macro lenses

Discussion in 'Digital SLR' started by Troy Piggins, Jul 24, 2008.

  1. Troy Piggins

    Troy Piggins Guest

    I've been meaning to do this for months. Finally took the
    opportunity. Wanted to take shots of a measurable subject at
    different magnifications to:

    - show what 1:1 really means (even though I know)
    - measure the real magnification of extension tubes on my macro
    lens, other than saying it's about 2:1
    - see what the magnification of extension tubes is at infinity
    focus on my macro lens.

    Lately I've been shooting with full set of extension tubes on,
    and I realise you lose infinity focus, but I've been wondering
    what the minimum magnification really is.

    All shot with Canon EOS 30D (sensor size 22.5mm x 15.0mm), EF
    100mm f/2.8 Macro USM lens. Extension tube set was Kenko 68mm
    full set. I didn't bother testing individual tubes because I have
    never used less than the full set since I want them for maximum
    magnification, and also because testing the various combinations
    of 3 different length tubes would drive me nuts.

    I realise it's probably not the most accurate test. If I'd shot
    with the ruler across the diagonal it'd be a little more precise
    because when scaling things, the longest measurable distances are
    the best. I also could have used a tripod and made sure the scale
    was dead level. But I figure it's near enough for my purposes and
    still helpful for others.

    So here we go.

    Bare 100mm macro lens, 1:1 magnification. Near enough to
    22-22.5mm on the scale, 22.5mm sensor width, so the 1:1 mag seems
    correct.
    http://piggo.com/~troy/photos/00_equipment/magnification/img_8750.jpg

    100mm macro lens with 68mm of tubes, focused to minimum distance.
    Near enough to 11mm, 22.5mm sensor width, so 2:1 mag seems about
    right.
    http://piggo.com/~troy/photos/00_equipment/magnification/img_8748.jpg

    100mm macro lens with 68mm of tubes, focused to infinity. Near
    enough to 34mm on the scale, 22.5mm sensor width, so around 2:3
    or 1:1.5 magnification. Keep in mind the lens is focused to
    infinity, but this shot is all that is in focus due to the tubes.
    Everything more than a couple of millimetres behind it is out of
    focus.
    http://piggo.com/~troy/photos/00_equipment/magnification/img_8749.jpg
     
    Troy Piggins, Jul 24, 2008
    #1
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  2. Troy Piggins

    jimkramer Guest

    But testing the 100mm with tubes is sooooo much fun!!!
    http://www.jlkramer.net/Pictures/100mm/100mmTest.htm
    -Jim
     
    jimkramer, Jul 24, 2008
    #2
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  3. Troy Piggins

    Troy Piggins Guest

    * jimkramer wrote :
    :) Good tests. Wish I'd seen them earlier, but I still would
    have done my own. I don't understand inches, I'm all metric
    baby! I also wanted to understand it all in terms of
    magnification. Perhaps you could add that sort of info to your
    page.

    Thanks for sharing. Bookmarked. :)
     
    Troy Piggins, Jul 24, 2008
    #3
  4. Troy Piggins

    jimkramer Guest

    Inches are just like mm only 25.4 times as big. :)
    -Jim
     
    jimkramer, Jul 24, 2008
    #4
  5. I have no series (and certainly no art <g>) to contribute but a few weeks
    ago I just had to see what this setup would do[1]: D60, 18-55mm (at 18mm)
    reverse-mounted on the front of 55-200mm (zoomed in until the image was no
    longer inside a black circle <g>). These are mm marks on a wooden ruler;
    the image is not cropped.

    http://blinkynet.net/stuff/mm_marks.jpg

    Thank God for the new rails. :)

    [1] There was probably math to do this, but, you know... :)
     
    Blinky the Shark, Jul 24, 2008
    #5
  6. Troy Piggins

    Troy Piggins Guest

    * jimkramer wrote :
    You whacky Americans. What will they think of next.
    Sounds like a catchy system of measuring. It should really take
    off.

    Ok, I googled it. 12 inches to a foot. 3 feet to a yard. 1760
    yards to a mile. It's so easy to remember. I don't know why us
    in the rest of the world are using this silly metric system where
    it's 1000mm to metre, 1000m to km. :-D
     
    Troy Piggins, Jul 24, 2008
    #6
  7. Overheard (really!) in a Navy ROTC course* at a well-know institute of
    higher education in the US.

    Professor: We will now compute the density of sea water in slugs per cubic
    yard.
    Cadet: Sir! Excuse me, sir! But, sir! Are you serious or making a joke, sir?
    Professor: I'm terribly sorry, but I'm serious.

    *: Air, Water, and Interface Vehicles. A seriously great course for anyone
    even vaguely interested in boats.
     
    David J. Littleboy, Jul 24, 2008
    #7
  8. Troy Piggins

    Troy Piggins Guest

    * Blinky the Shark wrote :
    That's pretty big magnification! Impressive. Understand now how
    hard it must've been to control.
     
    Troy Piggins, Jul 24, 2008
    #8
  9. Rails and remote IR shutter release. Won't be shooting any busy bees with
    that 12:1 setup. :)

    http://blinkynet.net/stuff/compound.jpg
     
    Blinky the Shark, Jul 24, 2008
    #9
  10. Yours are all so similar...this-m, that-m, some-other-m. No wonder
    they're so confusing! :)
     
    Blinky the Shark, Jul 24, 2008
    #10
  11. Troy Piggins

    Annika1980 Guest

    I was out trying to shoot eagles one day and I had the trusty old
    Vivitar 2x on the 400 f/5.6. But for some stupid reason I couldn't
    get the damn lens to focus, even manually. My 400 f/5.6 has some
    focus problems anyway (it slips when focusing manually so using TCs
    becomes quite a challenge), but all I was getting was a blurry
    screen. I checked every setting I could think of and couldn't figure
    out what the hell happened.
    I even went through all the Custom Functions to see if I might have
    set something screwy. Then I finally noticed that the 2x wasn't the
    2x at all, but was actually my Kenko 36mm extension tube that is the
    same size and color as the 2x.

    Oops!
     
    Annika1980, Jul 24, 2008
    #11
  12. Troy Piggins

    Troy Piggins Guest

    * Annika1980 wrote :
    :) Haven't heard that one before! I've got the Canon TCs.
    They're white, metal, and much heavier than the Kenko black
    plastic tubes. :)
     
    Troy Piggins, Jul 24, 2008
    #12
  13. Troy Piggins

    Peter Irwin Guest

    If he allows for a slight approximation then this is actually
    a pretty good question for remembering useful facts.

    - density of seawater is 64 pounds per cubic foot
    - acceleration due to gravity is a little over 32 feet/second^2
    - Therefore very nearly 2 slugs per cubic foot of seawater
    - 27 cubic feet in a cubic yard
    - Therefore nearly 54 slugs per cubic yard of seawater

    Now if he insisted on a more exact answer of 53.7something,
    the simplicity of the question would be lost, but if "nearly 54"
    is a good enough answer then it is good practice for quick mental
    calculations and remembering acceleration due to gravity and
    the density of seawater.

    Peter.
     
    Peter Irwin, Jul 24, 2008
    #13
  14. Troy Piggins

    savvo Guest

    Don't forget furlongs and chains otherwise you'll never know what an
    acre is.
     
    savvo, Jul 24, 2008
    #14
  15. Troy Piggins

    Mark Thomas Guest

    what about 3 barleycorns to the inch?
    rods, poles and perches?

    ...and fathoms and nautical miles, of course.
     
    Mark Thomas, Jul 24, 2008
    #15
  16. Troy Piggins

    jimkramer Guest

    New focusing rails? If so, what did you wind up with? My Novaflex set just
    doesn't cut it most of the time. :-(

    -Jim
     
    jimkramer, Jul 24, 2008
    #16
  17. Blinky the Shark, Jul 24, 2008
    #17
  18. That's outta my ... league.
     
    Blinky the Shark, Jul 24, 2008
    #18
  19. Troy Piggins

    bino Guest

    They all look good to me!
     
    bino, Jul 24, 2008
    #19
  20. One of the forgotten purposes of the supposedly silly old unit systems
    was to make mental arithmetic easy. For example a circle seven yards in
    diameter was a chain in circumference, a chain being handy for
    measuring the length of curves.
     
    Chris Malcolm, Jul 30, 2008
    #20
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