This solidly made and versatile set of extension tubes are designed to enable a lens to focus closer than its normal minimum focusing distance. Getting closer has the effect of magnifying your subject, making it appear larger in the viewfinder and in your pictures. They are exceptionally useful for macro photography, enabling you to convert almost any EF or EF-S lens into a macro lens at a fraction of the cost while maintaining its original optical quality.
The Kenko DG Extension tubes have no optics. They are mounted in between the camera body and lens to create more distance between the lens and sensor. By moving the lens further away from the camera's sensor, the lens is forced to focus much closer than normal. The greater the length of the extension tube, the closer the lens can focus.
In this set are three tubes - 12mm, 20mm, and 36mm - which can be used individually or in any combination to obtain the desired magnification. Kenko's AF extension tubes are designed with all the circuitry and mechanical coupling to maintain autofocus and TTL auto exposure with most Canon lenses, so there is enough light to activate the camera's AF system properly. And if the light levels are insufficient, you can switch to manual focusing and still achieve the results you are after.