Get Close With Extension Tubes

Lenses focus more closely by moving elements further from the image sensor or film. Extension tubes are hollow tubes that move the whole lens farther away from the image sensor or film. This allows the lens to focus much more closely, increasing the magnification. Most extension tubes also have the electrical and/or mechanical connections to allow the lens to auto-focus and auto-expose.

This photo was taken with a Canon 55-250mm kit lens set at 200mm and closest focus.

Most lenses will focus to a magnification of between 1/10 to 1/4 life size at their closest focus setting. The formula for extension is that when a lens is focused at infinity, extension equal to the focal length of the lens will produce a life sized image on the sensor or film(this assumes a full-frame sensor, magnification will be higher for APS sized sensors). Thus, 50mm of extension tubes behind a 50mm lens focused at infinity will produce a life sized image.

Canon 55-25-mm at 200mm with 12mm extension tube between camera and lens.

Advantages of using extension tubes for close focus work:
     *Extension tubes sets are much cheaper than any dedicated macro lens
     *They are lightweight and smaller than most macro lenses
     *Tubes work with any lens that you already own
     *Extension tubes add no interference to the optical path and require little extra exposure
     *They do not change the apparent focal length of the lens used with them
     *Tubes allow a choice of working distance when used with a zoom lens

Canon 55-250mm at 200 with 20mm extension tube

Cons of extension tubes:
     *Lenses mounted on extension tubes will no longer focus to infinity
     *Lenses have a very limited focusing distance range when using extension tubes
     *Camera can feel awkward and unbalanced even on a tripod because the lens is physically extended away from the camera body.
     *Extension tubes will not work with very short focal length lenses because the focus point is placed behind the front lens element.
     *Some extension tubes might limit auto-focus and auto-exposure/metering pattern options.
     *Tubes are much less convenient to use and less versatile than a dedicated macro lens.

55-250mm lens at 200mm with 36mm extension tube

General advice for close focus work:
     *Just like with telephoto lenses, camera shake and subject motion are both magnified along with subject magnification. Either fast shutter speeds in combination with image stabilization or a sturdy tripod are required to get sharp images. I much prefer tripods, manual focus, small apertures, low ISO's and slow shutter speeds for maximum image quality.
     *A good ball head on the tripod makes setting up the shot and locking down a front-heavy camera much easier. To me, nothing is more frustrating than continually needing to readjust the camera because the head is not heavy enough and the frame keeps creeping down between or during exposures. Having to loosen and tighten several different knobs or levers to make a simple framing adjustment seems wasteful when a ball head is so much easier and faster.
     *My personal experience has been that 50mm and 85mm prime lenses both make great macro lenses when used in combination with extension tubes. This is especially true for APS sensor DSLR's.

55-250mm lens at 200mm with 48mm extension

It can be less than convenient to have to remove a lens from the camera, attach an extension tube and then re-attach the lens in order to get a macro shot. If the next shot is a heron 30 feet away, the whole process needs to be reversed. If the selected tube does not get you close enough, another tube must be added for more extension. This can be a slow and awkward process in the field, especially when working on the beach or in a swamp with no place to set things down.

55-250mm lens at 200mm with 56mm extension

Mostly I still choose to carry a set of three(12mm, 20mm and 36mm) extension tubes over a dedicated macro lens. I don't do a huge amount of macro work and the trade-offs are worth it to me. I know my lenses, both primes and zooms, and how they will "see" with a given amount of extension. When needed I can go larger than life size, which hardly any dedicated macro lenses can do.

55-250mm lens at 200mm with 68mm extension

If you want to try true macro photography but have a limited budget, extension tubes will allow you to get your toes wet without breaking the bank. If macro is something that you absolutely fall in love with you can always purchase a dedicated lens later. But you might also be able to do everything you want to do with extension tubes.