Buy from Amazon.com : http://fave.co/191g1xR

Vivitar Series 1 2X Teleconverter (7 Elements) for Canon EOS

Product Description :
Multiply the focal length of your lens by 2 times
Minimum focus distance is maintained so the lens behaves as a macro lens
Retains Auto Exposure modes
Compact Lightweight
Inexpensive - keeps you one step ahead of your longest lens