Use of extension tubes for better lighting

The photos in this post of Tetracha floridana (Florida Metallic Tiger Beetle) illustrate a technique that I have begun using recently to improve the lighting in my full-flash insect macrophotographs—use of extension tubes!  I know this sounds strange, and I actually just stumbled onto it myself when I started using extension tubes in combination with my Canon EF 100mm macro lens.  Okay, I can hear it now: “Why not use the Canon MP-E 65 mm macro lens?”  It’s a good question, as at magnifications above 1X there is no finer lens than the 65mm.  However, the tiger beetles that I spend a lot of time photographing are right in that size range where sometimes I need magnifications below 1x (whole body shots of medium to large species), while other times I need magnifications above 1X (small species and closeups—particularly face shots).  Fortunately, the entire spectrum of magnifications (up to 5X) is covered by these two lenses, but there is, unfortunately, no overlap.  This is where the extension tubes come in—when all 68mm are added the 100mm lens effectively changes from a 1.0X–∞ lens to a 0.7–2.0X lens.  This gives a frame width of 11–33 mm, perfect for nearly all North American tiger beetles (most species range from 6-20 mm, excluding legs and antennae). 

In addition to allowing a more appropriate range of magnifications without the need to switch out lenses, this has one other effect—it moves the lens a little closer to the subject.  That in itself is of no particular benefit, but since I use the front-of-the-lens-mounted Canon MT-24EX dual flash, it also moves the flash a little closer to the subject.  It’s not a huge distance, only about 20 mm, but keep in mind that the flash heads extend forward from the front of the lens (especially with the Kaiser shoes that I use with my diffuser), and the front of the diffuser itself lies at about 60 mm in front of the lens face.  Thus, at 1X the the front of the diffuser sits ~80 mm from the subject with the 100mm lens only, but with 68 mm of extension tubes added it sits only 60 mm from the subject.  The closer the light source is to the subject, the greater the apparent light size, and larger apparent light size results in more even lighting with reduced specular effects.

Tetracha floridana | Pinellas Co., Florida (100mm lens only)

100mm lens + 68mm extension tubes

100mm lens only (slightly cropped)

100mm lens + 68mm extension tubes

The primary disadvantage to doing this is loss of ability to focus to infinity.  Frankly, this is functionality I never used with the 100mm lens, preferring instead the 17-85mm wide-angle lens for more general landscape and habitat photos.  The other downside is that placing the lens closer to the subject can result in greater chance of “spooking” the subject and causing it to flee or behave evasively.  Again, however, my experience is that if a subject can be photographed at 1X with the 100mm lens, it can be photographed at 2X with the 100mm lens + extension tubes.

Has anybody else ever tried this, and if so what was your experience?

Copyright © Ted C. MacRae 2011

17 thoughts on “Use of extension tubes for better lighting

  1. I don’t have any extension tubes, so I’ve never even considered this. Did you try any comparisons of the 100mm+tubes at 2x versus the 65mm at 2x? I’m curious if you see any differences in quality.

    • I haven’t done that comparison, and even the above photos weren’t done as a direct comparison but rather with different beetles just trying different things. I didn’t notice the effect on lighting until I was reviewing the photos later.

      I’m still trying to work up the nerve to try extension tubes on the 65mm!

  2. So……
    You’re telling me that I need to do more than:
    1. Put the bug in the palm of my left hand.
    2. Pick up the camera in my right, and mash the little “smiley-face” button.
    3. Walk over to the window, hold my hand in the sunlight, aim the camera at my left hand, and
    4. Push the little round button?

  3. Hey Ted.
    I have the same camera and 100mm lens you use and I was wondering what brand of extension tubes you have and why you chose them? (I’m still saving for the MT-24EX flash and I know that is the critical component.)

    Thanks for your help and inspiration to all us other bug photographers.

    • Thank you, Tracy! I have the Kenco Auto Set – not the cheapest, but has all the electrical contacts to allow flash metering.

      There are some who are abandoning the MT-24EX twin flash in favor of the Speedlite 580EX held out over the lens on a bracket. The greater apparent light size one can achieve by doing this and availability of soft box diffusers for this flash make it an attractive alternative to the twin flash. My main complaint, however, are the deep shadows under the subject that the twin flash greatly reduces. If I had to do it all over again, I’d still go with the MT-24EX.

  4. Nice demonstration Ted!

    With my Nikon set up, the only option to get beyond 1X is extension tubes (insert a little Canon-envy here), and I’ve noticed some reduction in image quality with them in play. Not a lot, but it is there. There is also a vast reduction in depth of field with the tubes – makes me pay very close attention to composition so I maximize my focal area! For that reason, I only tend to use them when absolutely necessary (i.e. small, small flies).

    • Thanks Morgan. I’m not sure I understand how extension tubes could reduce image quality since they’re just a hollow tube and have no glass, but I’m no expert about these things either.

      Can’t you counteract the DOF by increasing the f-stop? (Assuming you have electrical contacts in your extension tubes).

  5. Pingback: My Canon 8X Macro Lens « Beetles In The Bush

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