Extension Tubes
XTENSION TUBES are accessories that you place in between the camera body and the lens to gain magnification. They are hollow tubes, meaning you aren’t adding any additional glass elements that could adversely affect image quality. They come in a range of sizes—12mm, 20mm, 25mm, and 36mm—and can be stacked together or used singly. And yes, even those of you who have bought an actual macro lens should still buy at least one extension tube—if not a set of three extension tubes. You can, of course, buy just one. Just ask Canon or Nikon, and they’ll be happy to sell it to you, but where’s the logic in that? Why buy Canon’s single 25mm extension tube when you can buy a set of three extension tubes from Kenko for about only forty bucks more? With Kenko, you’ll get 12mm, 20mm, and 36mm extension tubes, and all of the “pins” (the contacts, see below) are there, so it matches up with the Canon body and lens it’s used with, and you don’t have to worry about “losing” your metering. This same set of three extension tubes is also available for Nikon and Pentax shooters at the same price. When you use all three tubes together, you have a total of 68mm of extension available, and that’s roughly three times more extension than one Canon 25mm extension tube. That translates into even greater degrees of magnification.
So, just how does an extension tube work? Simply put, the mechanics of most any lens work as follows: The farther away the rear element of a lens from the CCD or film plane, the closer the lens will focus. So, in theory, when you focus on something close—let’s say, your daughter sitting in her high chair eating her oatmeal—the rear element of your lens has moved farther away from the CCD or film plane. So it stands to reason that if you could place some kind of spacer between your lens and camera body, you should be able to focus closer. This is why you could take that toilet paper core and, with an ample amount of duct tape, secure it between your lens and camera body and fashion an instant super-close-up lens!
A NOTE ABOUT EXTENSION TUBES AND WIDE-ANGLE LENSES
A wide-angle lens for a digital camera (such as the 12–24mm range) or a wide-angle lens meant for a 35mm film camera (the 17–28mm range, for example) will not be able to focus with any extension tube because the focus point is now so close that you would literally have to climb inside the lens to find it.
The drawbacks to this are, however, far greater than the advantages: Although extremely lightweight, a toilet paper core doesn’t hold up well in the rain, for example. It also is much lighter in color than the black camera body and lens; this is enough contrast to scare away macro subjects. And a toilet paper core is missing the pins (the contacts on extension tubes that are necessary to maintain wide-open viewing), so when you stop the lens down to increase your depth of field, the image in your viewfinder gets really dark. So the long and the short of it is, forget the toilet paper core and go with the heavy metal look of extension tubes, which are impervious to rain and do have the necessary pins that allow you to maintain wide-open metering.
Okay, so now you place just one extension tube between your camera and lens and you “push” the rear element of the lens farther away from the film plane; this affords you a closer view, a greater magnification, of what lies before you. And when you stack extension tubes, adding one on top of the other, your subject becomes even larger, since you’re afforded an even closer view. Extension tubes are wonderful, and must-have, additions to that telephoto zoom “with macro” that you already bought. An 36mm extension tube (or multiple extension tubes) in combination with your street zoom or telephoto zoom with macro allows you to record an extreme close-up—if not a macro shot (See here for more on magnification ratios and extension tubes.)
The only drawback to extension tubes is the decrease in light that comes with their use, which in turn affects viewfinder brightness and exposure times (requiring slower shutter speeds). Yet even these two very minor drawbacks are not reason enough to forgo buying extension tubes.
Let’s assume you have a street or telephoto zoom lens with a macro function. Chances are good that you can record an image at 1/6 to 1/4 life size, and chances are even better that you’ve already done so and made the discovery that many times you can’t get as close as you want. All that’s missing is a set of extension tubes! Dewdrops on blades of grass or flower stems continue to be subjects that many shooters eventually migrate toward, but often, the results are far from fulfilling as the photographer quickly learns the macro feature on these zoom lenses is hardly macro at all. With the aid of some extension tubes, however, a macro shot is just a few twists away.
For these examples, I was shooting at 50mm. (If you’re shooting digitally, set the focal length of your street zoom to 35mm, which will be the rough equivalent of a 50mm lens, and if you’re shooting with a film camera, set the focal length to 50mm.) With my 18–70mm street zoom at a focal length of 50mm and with one 12mm extension tube, I was able to record dewdrops on a lone flower stem but was still too far away for my taste (top left). This image is at about a 1:4 magnification ratio, or 1/4 life size. When I combined the 12mm extension tube with the 20mm tube, I approached a life-size magnification and got closer to a far more fulfilling composition. But it wasn’t until I placed three extension tubes (a 12mm, a 20mm, and a 36mm) between the camera and lens that I went beyond life size (since the extension of 68mm exceeded the focal length of 50mm) and fully realized a frame-filling composition. The third image is at about 1.3X life size. In fact, the dewdrops are so close that you can see within the droplets the landscape that lies behind them. Note that for all exposures I used a tripod and the camera’s mirror lock-up feature with an electronic cable release.
Let’s consider just how big this is in terms of magnification: Focal length “over” mm length of extension tubes equals magnification size. If 50mm “over” 50mm of extension equals 50/50 or 1 (1:1, or life size), and we have a 50mm focal length “over” 68mm of extension, that gets 50/68 or 1.36:1—just a bit more than 1.3X life size.
Top left: 18–70mm lens at 50mm with 12mm extension tube, ISO 200, f/22 for 1/15 sec.; top right: 18–70mm lens at 50mm with 12mm and 20mm extension tubes, ISO 200, f/22 for 1/10 sec.; bottom: 18–70mm lens at 50mm with 12mm, 20mm, and 36mm extension tubes, ISO 200, f/22 for 1/6 sec.
The dewdrops also help illustrate the drawback to extension tubes. If you’re using all three extension tubes at one time with a moderate zoom or telephoto zoom and, of course, are on a tripod, your camera and lens will experience some serious wobble—or camera shake—if you press the shutter manually. So, if you’ve ever wanted a great excuse to use a cable release and mirror lock-up, this would be it!
In the first photograph, I pressed the shutter release with my finger, and that, of course, introduced the wobble factor. Since the shutter fires right away after pressing the shutter release, the exposure records the wobble and not tack-sharp drops of dew on a flower stem. In the second photograph, I chose to use mirror lock-up and my electronic cable release.
And finally, don’t even bother trying to use the depth-of-field preview button, as the length of extension tubes coupled with a moderate or telephoto zoom will now render an exceptionally dark view as you look through the viewfinder—so dark, in fact, that you might think your camera is broken. (See here for more on depth-of-field preview.)
Both photos: 50mm lens, with 12mm, 20mm, and 36mm extension tubes, f/22 for 1/4 sec.
One of the situations in which I use an extension tube is when shooting flowers with a telephoto lens. For years I had used my 300mm lens with one 36mm extension tube, and this combination would always “knock out” my backgrounds of surrounding flowers into wonderful areas of out-of-focus tones and color. Several years ago, however, I picked up Nikon’s truly amazing 200–400mm tele-zoom lens, and it has since replaced the 300mm lens of yesteryear.
Like most telephoto zooms, the 200–400mm also can focus quite close, rendering a reproduction of roughly 1:4 (or 1/4 life size), and it can do so at all focal lengths. Still, the 200–400mm will seldom fill the frame with that lone flower. But with the addition of that one extension tube (the 36mm), I can once again isolate a lone flower against a background of blurred color. Take a look: With the lens at a 300mm focal length but no extension tube, I was certainly able to isolate this lone Iceland poppy, but not without also recording some competition both from background flowers and from stems that created some distracting lines. The eye is forever intrigued by line, drawn to it like a moth to flame, as they say. Unfortunately, this image is not about line but about color and texture, and I wanted a frame-filling flower shot.
Adding the 36mm extension tube was the simple solution. This gave me options: I could either leave the lens at 300mm and walk closer to the flower, or I could stay put and shift toward the 400mm focal length to bring the flower closer to me. In this case, I did the latter, and as you can clearly see, the second image is all about a lone Iceland poppy. I shot both images at f/7.1 to maintain a background of tones and shapes, but I adjusted the shutter speed: The first was correctly exposed at 1/320 sec., while the second image, due to the addition of the 36mm extension tube, needed 1/250 sec.
EXTENSION TUBES VS. TELECONVERTERS
Do not confuse extension tubes with 1.4X, 1.7X, or 2X teleconverters, multipliers, or doublers, as they’re often called. Unlike a teleconverter, which does have optical glass in its construction, an extension tube is glassless, as mentioned here. It is nothing more than a piece of metal that places more distance between your camera body and lens (a metal toilet paper core, if you will).
A teleconverter, with its piece of glass, on the other hand, increases the focal length of a given lens by 1.4, 1.7, or 2 times and introduces a possible loss of sharpness if the optical quality is not “matched” to the lens in use. That’s why, and of course this is just my opinion, you should use only those converters that are designed and built by the same folks who built your lens. If you have a Nikkor lens, then use only a Nikon converter.
So just by way of example, a 2X teleconverter would change a 100mm lens into a 200mm lens.
You should give very serious consideration to using a Nikon TC1.4B or TC1.7B teleconverter (1.4X and 1.7X teleconverters, respectively) with your Nikkor 70–200mm F2.8 zoom lens, along with a 36mm extension tube. You’ll begin to see and record some truly beautiful and muted tones of background color when shooting those lone flower compositions in the wild or at the local park, if not in your own backyard. Ditto to Canon, Pentax, Sigma, and Tamron users.