Tubes made from metal and, more frequently, plastic inserted between the lens and the camera, thereby making the lens to film distance greater. The result is increased magnification for close-up photography.
A set of rings or tubes of varying lengths, used between the camera body and lens to permit focusing the lens on subjects at close range.
These are a handy way to turn any long lens into a macro lens for ultra-close shooting. They are hollow metal tubes that are mounted between the camera and the lens. Typically they come in a set of different lengths which can be combined. It is a good idea to open up the lens a little when using an extension tube, as a little light is lost. It should be noted that they do not work when used with wide lenses. [Go to source