The Kenko Auto Extension Tube Set DG contains three tubes of different length--12mm, 20mm, and 36mm--which can be used individually or in any combination to obtain the desired magnification. Actual magnification effect changes with each specific lens. The greater the length of the extension tube, the closer the lens can focus.
They are mounted in-between the camera body and lens to create more distance between the lens and film plane by moving the lens father away from the film, or CCD sensor in the camera.
Extension tubes are designed to enable a lens to focus more closely than its normal set minimum focusing distance. Close focusing has the effect of magnifying your subject; making it appear larger in the viewfinder and in your pictures.
Telephoto lens shooter use extension tubes when their subject is inside the minimum focusing distance for the lens. The tubes are also useful for macro photography, enabling you to convert almost any lens into a macro lens at a fraction of the cost while maintaining the lens's original optical quality.
The DG extension tubes have no optics. They are mounted in between the camera body and lens to create more distance between the lens and film plane by moving the lens father away from the film, or CCD sensor in the camera.
Available for Canon and for Nikon.