From Canon USA:
Thank you for using Canon products.
We have determined that some units of the EF 200-400mm f/4L IS USM Ext. 1.4x interchangeable lens for digital SLR and mirrorless cameras exhibit a phenomenon in which the focus may not be achieved during AF shooting. Firmware which addresses this phenomenon is available for download below.
We would like to offer our sincere apologies to users who have been inconvenienced by this issue. Going forward, we will spare no effort in our quality management to make sure our customers can use our products with confidence.
When using this lens with some camera models* and performing AF shooting from approximately 3m, the subject may not be in focus in some occasions.
* Camera models: EOS-1D X Mark II, EOS-1D X, EOS-1D C, EOS 5Ds, EOS 5Ds R, EOS 5D Mark IV, EOS 5D Mark III
Download Firmware Version 1.1.0 for the EF 200-400mm f/4L IS USM Extender 1.4x
- Canon EF 200-400mm f/4L IS USM Extender 1.4x lenses with Firmware Version 1.0.0
Customers who own one of the affected camera models above, or one of the cameras** that can be used for the lens’ firmware update can download the latest firmware version and then perform the lens’ firmware update using the camera.
** EOS-1D X Mark II, EOS-1D X, EOS-1D C, EOS 5Ds, EOS 5DsR, EOS 5D Mark IV, EOS 5D Mark III, EOS 6D Mark II, EOS 6D, EOS 7D Mark II, EOS 80D, EOS 70D, EOS Kiss X9i, EOS Kiss X9, EOS Kiss X8i, EOS Kiss X7i, EOS Kiss X7, EOS Kiss X6i, EOS M6, EOS M5, EOS M3, EOS M2, EOS M, EOS M100, EOS M50, EOS M10. Please note that EOS M camera models require an adapter EF-EOS M to connect to the EF 200-400mm f/4L IS USM Extender 1.4x lens.
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This information is for residents of the United States and its five territories only. If you do not reside in the USA or its five territories, please contact the Canon Customer Support Center in your region.
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Canon U.S.A., Inc