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 for the Uniplus Tube 25 is about 1/2 when used with a 50mm standard lens.
Provides 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 digital SLR's and some of the digital SLR lenses.