In Microsoft Windows 7, Clone Mode (same image on both the ThinkPad LCD and an external monitor) may not function when using the Fn + F7 key combination on ThinkPads that have Optimus graphics. Depending upon what combination of display devices are being used, Optimus may use two different video adapters: integrated Intel graphics and discrete NVIDIA graphics. Because two different graphics adapters may be in use, Windows 7 may not be able to correctly set up Clone Mode.
Any of the following systems with NVIDIA Optimus graphics, running Windows 7, where the machine is set in BIOS to run in Optimus mode:
The following shows what display ports are controlled by the different display adapters. If the display configuration you are using involves both the Intel and NVIDIA graphics adapters, Fn + F7 will not work correctly.
ThinkPad T420, T420i, T420s, T420si, T520, T520i
Clone Mode in Optimus using two graphics adapters is only supported and configured through the NVIDIA Control Panel. It can not be enabled by using the Windows display control (Fn + F7) or the Intel display control panel.