Choosing Camera Extension Tubes for Macrophotography
Camera extension tubes allow you to take close-up photos of tiny objects by increasing the effective magnification of your lens. These tubes, sometimes called extension rings, are available in various thicknesses, and together with the lens focal length and its close focusing distance, determine the degree of enlargement. They're suitable for use with macro lenses, as well as with any lenses with moderate focal length.
How Camera Extension Tubes Work
When you focus, you move a lens group backward and forward until the rays of light are perfectly in focus on the camera sensor. As you move closer to your subject, the focusing lens moves farther away from the camera's sensor, which is why close focus lenses often extend from the camera as you focus. Based on lens design, there's a natural limit to how close you can focus. This is where an extension tube comes in, because it moves the lens farther from the camera. The longer the extension tube, the closer you can focus and the greater the magnification, limited only by how close you can get the lens to your subject.
Maintaining Camera Functions with Lens Extension Tubes
Digital cameras use electronic signals to control lens functions such as focus, aperture, and image stabilization. For this reason, most types of extension rings contain matching contacts that transfer signals from the lens to the camera. There's a wide choice ranging from OEM Canon extension tubes to numerous third-party tube suppliers. It's important to check that bayonet couplings are a good fit, as any looseness affects camera-to-lens communication. Sets are available for most camera mounts, including Sony, Pentax, and Nikon extension tubes.
Magnification with Macro Extension Tubes
The degree of magnification depends on lens focal length and the size of the extension tube. With macro lenses, it's often possible to achieve 2.5 times full life size, and 1.5 times magnification is practical with standard lenses. For various reasons, most photographers find lenses between 30mm and 100mm work best, but there are no hard-and-fast rules. In practice, the low magnification of ultra wide-angle lenses together with their physical size limits the amount of magnification possible, while the length and lack of rigidity of extension tubes limits the magnification possible with long lenses. A way to overcome the limitation with telephoto lenses is to consider using camera macro accessories like bellows mounted on slider rails.
Alternatives to Extension Tubes
Apart from extension rings, there are several other ways to do macrophotography without a dedicated macro lens. One idea is mounting close-up lens filters to your camera lens. These magnify the image and are particularly effective with long lenses. Another method is to use lens reversing rings to turn your lens around. This works well if you have an older lens with manual controls that allow you to adjust the aperture. A third solution is to use SLR camera macro couplers to join two lenses together. Similar in concept to using a reversing ring, this method allows you to determine the magnification, and to use the primary lens to adjust your focus and aperture.