Chosen Solution
Hello, iMac Retina 5K 27" Late 2015 and iMac 21.5" Late 2012 I’m a graphic designer and photographer. I work primarily on an iMac (Retina 5K, 27", Late 2015). But we have an older iMac in the office that I’d like to use as a secondary monitor a iMac 21.5" Late 2012, so that I can work on two screens. I connected the two with a Thunderbolt to Thunderbolt cable and tried to connect through Target Display Mode by pressing command + F2 (I also tried command + fn + F2), and no dice. I realize the Retina 5k is not supported as a display via TDM so I can’t take the older iMac and display it on the Retina 5k one. But I should be able to display the Retina 5k iMac on the other one, right? Do I have this all wrong? Can the retina 5k not be used at all? If it can what could be the issue? Help! I’ve been trying to figure this out forever.
First, I do believe the cable needs to be a MiniDP Vs a Thunderbolt for it to work. The Apple TN is not complete. Heres the Apple TN that goes over what works and what doesn’t from Apples perspective: Use your iMac as a display with Target Display Mode
