The Kenko 25mm Uniplus Tube DG (extension ring) is an accessory exclusively designed for use with standard AF lenses to shoot subjects at closer distance with higher magnification. Magnification ratio and focusing distance effect vary according to lens and tube combination. The longer the tube, the stronger the effect.
The Kenko Uniplus Tube rovides perfect coupling with automatic aperture, TTL metering and AE mechanism. AF support is dependent on your lens' maximum aperture. As a rule, the lens has to be set to f/5.6 or brighter in order for the camera's AF system to work. This DG Extension tube has upgraded "Gate-Array IC" circuitry to work better with DSLRs and some of the DSLR lenses.