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Infobank

Lenses: Extension tubes

With many lenses, as you focus closer, the length of the lens increases. Or to put it another way, the lens moves away from the camera as the subject moves nearer to the lens. (Some lenses have a feature called internal focusing. Here, the elements move back and forth within the barrel, but the length of the lens does not change.)

The closest focusing distance is reached when the lens is extended as far as it will go. This focusing distance varies considerably from lens to lens, from 0.2m for the EF15mm, to 14m for the EF1,200mm. But the magnification of the subject (actually a reduction) stays within a narrower range, from about 0.1x to 0.3x.

Why do lenses stop extending? Partly because it costs more to design and manufacture lenses with longer extensions; partly because it is difficult to design a lens that gives high-performance results over a wide range of focusing distances.

Macro lenses

However, there are such lenses. The EF100mm, EF180mm and EF-S60mm macro lenses focus all the way from infinity down to a distance that gives 1x (life-size) magnification. If you use these lenses, you will find that the length changes considerably from one end of the focusing range to the other. (There is also an EF50mm Macro lens, but this requires the use of a life-size converter to give life-size magnification.)

Extension tubes

But you can increase the magnification of a lens simply by moving it further from the camera. All you need is an extension tube. This fits between the camera and the lens. There are no optical elements inside the tube − it is just a device to increase the lens extension.

Canon produces tubes in two different lengths − 12mm and 25mm. The EF12 and EF25 tubes come with electrical contacts which allow data transfer between the lens and camera to be maintained. It is possible to attach the EF12 tube to the EF25 tube to give a 37mm extension. Canon does not recommend this, as the data transfer may be affected, but acceptable results are possible if you are willing to experiment.

Mark II extension tubes

The Canon EF12 and EF25 Extension Tubes have been part of the EOS system since 1991. With no optical elements, little improvement is possible and so there was no need to bring out new versions.

However, September 2004 saw the introduction of the EOS 300D digital camera.

This featured a new EF lens mount. In addition to accepting all the past and current EF lenses, it also takes the EF-S lenses. These lenses do not fit the original EF extension tubes.

So at the same time the EOS 300D was launched, the EF12 II and EF25 II Extension Tubes were introduced. These can be used with EF-S lenses, as well as most EF lenses. And that’s the only difference. If you have the old tubes and do not use EF-S lenses, there is no need to upgrade.

The full area of a postage stamp, together with an image taken using the EF100mm lens fitted with the EF25 extension tube.

Compatibility

The Extension tubes are not compatible with the EF14mm, EF15mm and MP-E65mm lenses. In addition, the EF25 tube is not compatible with the EF20mm and EF24 f/1.4L lenses.

The tubes can be used with all EOS cameras, including digital, but there are slight exposure problems with some combinations of cameras and lenses. The instruction leaflet gives some guidance on this, but the best advice is to shoot some test frames with the camera and lens you intend to use and make a note of any exposure compensation that may be required. Keep this information safe for future reference.