Dorr Canon EOS Fit Auto Extension Tubes are designed to enable a lens to focus closer than its normal set minimum focusing distance. Getting closer has the effect of magnifying your subject (making it appear larger in the viewfinder and in your pictures). Dorr Auto Extension Tubes are exceptionally useful for macro photography, enabling you to convert almost any lens into a macro lens at a fraction of the cost while maintaining its original optical quality. Dorr Auto Extension Tube have no optics.
The Dorr Auto Extension Tube is 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 Dorr Auto Extension Tube, the closer the lens can focus. The Dorr 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. Dorr Auto Extension Tube's are designed with all the circuitry and mechanical coupling to maintain auto focus and TTL auto exposure with most Canon, Nikon, and Minolta lenses given there is enough light to activate the cameras AF system properly.