Changes in firmware
Firmware Version 1.0.4 is incorporated with the following correction
Firmware Version 1.0.4 is for lenses with Firmware Version 1.0.3 or earlier.
Lenses whose third digit in the serial number is “0”. (xx0xxxxxxx)
If the lens’ firmware is already Version 1.0.4, it is not necessary to update the firmware. The lens firmware can be checked through the menu on the EOS 5D Mark IV.