Cannot get duplication of screens to work with mini display between iMac & Macbook Have an iMac 21", 2.5, Mid 2011 and a MacBook Pro Mid 2012 and I just bought a Mini display to connect them through the Thunderbolt. I cannot see that they are connected or the choice to connect it in the screen logo in the menu bar. Command F2 doesn't work. 

Any idea whats wrong? how can I get the option to have them connected, not for data, just sound and image?
The problem is that you need to use a Thunderbolt Cable to use your iMac in Target Display Mode.  From Apple's website:



From your original question, you mention that you purchased a "mini display" which I can only deduce is that you meant that you bought a "mini Display Port cable."  If this is in fact the case, it's the wrong cable; which is why it's not working.