Hints for downgrading the EOS 5D Mark II firmware v1.2.4 to v1.1.0 Edit
- Read the Firmware Upgrade Guide by Canon (PDF) . The downgrade procedure should be the same.
- Get the original EOS 5D Mk II v1.1.0 firmware (self-extracting Windows exe-file)
- Be aware of the downgrade caution !!
- Note: don't keep more than one version of the firmware in the root directory of your CF card at the same time for starting with MagicLatern! It would cause an error message (without the orange box) of the update routine of the original v1.1.0 firmware and the camera would freeze with no effect by turning off the Power Switch. The only thing you can do than, is to detach the battery to force total camera reboot.
Downgrading the 550D firmware from 1.0.9 to 1.0.8 Edit
- Read this message from Pedro Barbosa and the 5D2 downgrade notes above
- Disable bootdisk flag in Magic Lantern 1.0.9's config file
- Install Canon's 1.0.8 firmware
- Install Magic Lantern for 1.0.8
Download link for 1.0.8 fw:  (thanks Pedro!)