How do i use my imac 21.5" 2011 as a display for my macbook pro late 2011, through thunderbolt cable ? I have tried and it doesnt seem to work, neither does target disk mode.

Sorry but only 27" iMacs can be used as external monitors.

You are correct, here is what Apple Says:

http://support.apple.com/kb/TS3775

I was able to find these instructions, however they referr to 2009-2011 27" iMacs. I think it's the same, if it's not then contact Apple directly for instructions. If either of the machines is less than 90 days old or covered by AppleCare then call AppleCare tomorrow for help, they should be able to easily answer this for you. You will find the number in your manual or you can use the AppleCare Contact Info link.

1. Your iMac should automatically recognize the presence of a digital video signal at the Mini DisplayPort and enter Target Display Mode.
2. If your iMac does not automatically enter Target Display Mode, press command + F2 to manually enter Target Display Mode.

BTW I found this thread, I think your solution is in there.

https://discussions.apple.com/thread/3363289?tstart=0

You did not mention if you tried the suggestion in the thread I provided. I would do that first!

Does it support the Late 2009 iMac Model? (21"). I have been trying to connect it but nothing changed

Yes, it does work. As I type this I am using an IMAC 21" screen as an external monitor for my 13.3 Macbook Pro. Here is how you do it:

1. Connect the Thunderbolt to both the your host (Macbook Pro) and your target(IMAC 21").

2. Enable Target Disk Mode by hitting CMND F2 on your IMAC. This will start the screen sharing.

3. You will see that the Macbook Pro is being read because if you scroll your mouse around on your Macbook pro, your mouse cursor will appear on the IMAC's screen. All you need to do is go into >System Preferences>Displays. Click on "Gather Windows" and this will bring up the IMAC display settings. Click on the check box "Mirror Displays" and that should do it.

Hopefully this works for you that are having issues connecting your Macbook Pro and IMAC 21" via Thunderbolt!

I still can't manage to do that.

My items:

1. iMac 21.5" Late 2009

2. Macbook Air 11" Mid 2012

3. Mini Display port to Mini Display port cable (not from the apple store)

From what I see everywhere, at the moment when you plug the cable into the macs, the display will be "refreshed" and than you can set it. However, it doesn't happen to my mac at all. I tried to key in the button CMND F2 but the only thing happens it the pointer is blinking (gone while i hit the keys)

So is every mini display port cable support thunderbolt?

The problem doesn't seem to come out from the macs

1. I tried to plug the mini display port to hdmi to a monitor for my macbook air and it works

2. I tried to plug the mini display port to mini display port to another macbook (pro in this case) and nothing works too.

I'm confused now

It's probably a bad cable. Or rather, a poorly engineered cable. Try an Apple cable instead.

Nicotangara,

You need a Thunderbolt cable, not a Mini Displayport cable. They have the same physical plug, but they are not the same.

So i have a Macbook Pro mid 2010 and i purchased a Imac 27" late 2012. By what i understood i cant put the i mac in target mode.

If i convert the miniport on the macbook pro to hdmi and the thunderbolt to hdmi could it work?