It is recommended that the latest application software be used, once the EOS-1D X is updated to the new Firmware Version 2.0.3 from older firmware (Versions 1.0.2 through 1.2.4).
Notes: Once the EOS-1D X camera is updated to Version 2.0.3, it cannot be restored to a previous firmware version (Version 1.0.2 through 1.2.4).
Fn5: Operation” “Custom Controls Menu”, is set to metering start only; depending on when the shutter button is half-pressed, it may initiate Auto Focus.
August 14th Firmware 2.0.8 is seen on a camera, but no details of what changed from V2.0.8 (via Canon Rumors) 2015 January 29th New firmware V2.0.7 – Improves the AF controllability when shooting in Live View mode with a wide-angle lens (fixed focal length or zoom).
Firmware Version 2.0.3 is for cameras with firmware Version 1.2.4 or earlier.
If the camera’s firmware is already Version 2.0.3, it is not necessary to update the firmware.
– Fixes a phenomenon in which, when shooting long exposures (several minutes), vertical lines appear on the right edge of captured images (still photos).