The 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, the lens is forced to focus much closer than normal. The greater the length of the extension tube, the closer the lens can focus.

The KENKO AUTO EXTENSION TUBE SET contains three tubes of different length, a 12 mm, 20 mm, and 36 mm, which can be used individually or in any combination to obtain the desired magnification. Kenko also makes a UNITUBE 12 mm or 25 mm which can be purchased individually.

Kenko's Auto Focus extension tubes are designed with all the circuitry and mechanical coupling to maintain auto focus and TTL auto exposure with most Nikon lenses given there is enough light to activate the cameras AF system properly.

Please Note;
1. When using extension tubes the lens will not focus to infinity. The focus range will be greatly limited to a very close focusing distance.
2. There is light fall off when using any extension tube, sometimes the equivalent of 3 f-stops of light is lost when using multiple extension tubes together. This light lost can affect the camera's ability to auto focus. Manual focusing is recommended should the lens begin to "hunt" (not lock onto the subject).
3. Nikon "D" information is not transmitted because the lens is focusing closer than its programmed to focus.
4. Kenko Auto Extension Tubes are not auto focus compatible with Nikon AF-s (Silent Wave) lenses, manual focusing is required with these lenses.