Extension tubes are tubes without any optical elements that you place between the camera and lens of an interchangeable lens camera. They extend the lens so it can focus closer, giving the lens macro capabilities. Some have full automatic couplings so the camera can continue to be used in all its auto and program exposure and focus modes. Some lower priced ones have no couplings, so the camera needs to be used in manual.
Tubes are often sold in sets of three. The set illustrated above has 13mm, 21mm and 31mm extensions, and these can be attached in any combination giving a total of seven different extensions:
- 34mm (13mm+21mm)
- 44mm (13mm+31mm)
- 52mm (21mm+31mm)
- 65mm (13mm+21mm+31mm)
Here a set of three tubes can be seen attached to a Nikon digital SLR camera.
This photograph of a British one pound coin was taken using a nikon camera with a 55mm lens set to infinity and an extension tube added. The smaller coin on the left is with the 13mm and the coin on the right is with the three tubes attached giving 65mm extension. The lens was at f/2.8 to show how shallow depth of field is. When using tubes you either need to use a very small aperture or shoot the subject parallel to the CCD or film plane. Here the coin was at an angle so only a shallow strip across the centre is sharp.
Advantages of using Extension Tubes
Low cost macro
No optical degradation
Disadvantages of using Extension Tubes
Limited magnification variations
Fiddly changing between magnifications
Taking lens off increases risk of dust intrusion
We have a selection of extension tubes in different camera fittings