The EF 2x II doubles the focal length of any lens it's mounted to, and reduces its effective aperture by two stops

Successors to the EF2x this model offers valuable improvements for further enhanced image quality. This extender allows users to combine practicality and functionality with a new optical system allowing them to extend the master lens focal length by 2x, with minimalloss of lens performance or image quality. With a dust- and moisture-resistant construction this extender has been designed to reinforce the EOS system. Specially designed to work in conjunction with the EOS-1V and IS super telephoto L-series lenses, it makes a highly dust- and water-resistant combination.
The EF2x II features improved anti-reflection materials inside the lens-barrel as well as improved coating around the outer edges of the lenses to reduce flare. All of these improvements will allow professional photographers to capture higher quality images than ever before.

• Outstanding optical performance that visually matches the images quality of the host lens.
• Maintains AF operation within aperture limits of camera body. (Combines f/8 for EOS-1V and EOS-3 - f/5.6 for other EOS models.)
• Maintains IS operation.
• High level water and dust resistance equivelant to the EOS-1V and Super Tele L Series IS lens range - suitable for use in heavy rain.
• O-ring seals protect the mounts and release lever.
• Reduces inner reflection for higher image quality