Extension tubes

Extension tubes are not used by a lot of photographers, but they offer two important functions. I always carry at least one tube with me wherever I travel.

Extension tubes are nothing more than hollow spacers. They don’t have any glass in them at all. They fit between the lens and the camera body, and they increase magnification. You can use only one of the tubes, or you can combine them in various ways. For the image of the gecko, below, taken during my frog and reptile workshop, I used two extension tubes in combination with a 50mm macro lens. The tubes increased magnification so I was able to fill the frame with the small, intriguing eye of the reptile. Of course, as magnification increases, depth of field is reduced. Therefore, whenever I’m doing macro work especially with extension tubes, I use the smallest lens aperture possible given the amount of light I have and the amount of movement on the part of the subject.

Extension tubes have another very important function. Many times when using a telephoto lens with subjects relatively close to the camera, the lens-subject distance becomes too small and you can no longer focus on the subject. Extension tubes address this problem.

For example, I set up a bird feeder just outside my office window. I put seeds on a flat pan and affixed a branch above the food for birds to perch on as they ate for natural looking images. The feeder was about 8 to 10 feet from my desk. I mounted the camera on a ballhead right next to me and set up a Canon 500mm f/4 telephoto with a 1.4x teleconverter. The latter magnified the focal length to 700mm. With this much glass, I couldn’t focus on the birds. The minimum focusing distance of the 500mm is 14.5 feet.

So, between the 1.4x teleconverter and the camera body I attached one extension tube. Suddenly, I could no longer focus to infinity, which was fine, but now I could focus on the birds at the feeder.

Extension tubes can be used with any lens (although they are typically not used with wide angles), and they reduce the minimum focusing distance. Again, depth of field is reduced, so to compensate I simply close the lens down as much as I’m able to given the amount of light that’s available. For the image of the blue grosbeak, above, my aperture was f/8. The blurred background was trees in the distance; it’s not an artificial backdrop. Extension tubes are inexpensive, light, and easy to carry. §