iMac as external monitor and brightness setting

Just in case people end up here looking for a solution for adjusting the brightness of an external monitor or iMac when connected to a macbook pro. I had the same issue as everyone in this forum. I have a late 2015 Macbook pro and I wanted to use my late 2009 i7 iMac as my monitor.

First issue

1. Don't use a Thunderbolt cable to connect the old iMac's display port. The only thing that works is a display port cable with dual male ends. This will work.

2. The whole F2 thing does not work so don't waste your time.

Second issue:

1. When I use my iMac as an external/additional display/monitor for my new Macbook Pro I can't control the brightness of my iMacs screen through the Macbook pro.

2. Instead of experimenting save time and go to the App store and purchase a program called ScreenDimmer.

3. Install this app and a dark screen icon will be added to your menu bar at the top right of your screen.

4. Click on it's icon and it will allow you to adjust the brightness of 3 separate, connected displays/monitors.

5. This will work trust me.

The suggestions work on some Macs but not others. Some seem to need OS 10.6.

I use Yosemite (OS 10.10) with mid-2012 MacBookPro and late 2009 iMac 27". I just got a newer 27" iMac (late 2013), and wanted to keep only one full size keyboard. My issue is Microsoft Word- that is associated with the hardware when installed so cannot be used with the newer iMac. My first solution to allow a larger display was to use my laptop with the old iMac as external monitor - not great because I still had to use the MacBookPro keyboard. I did not know Screen Sharing allowed you to actually run programs on the target Mac- that saved me! With old iMac as screen shared machine, I can use a full keyboard (plugged into the 2013 iMac) and run Word on the screen shared older iMac. Not that great for programs needing faster graphics response (like games), but very useful for Word, Powerpoint, etc. I drag down the screen image on the 2013 iMac and use the old iMac as the display when running Word. Saved me over $100 purchase of yet another copy of MS Office 2011. Yes, you do need desk space wide enough for two iMacs.

Give screen sharing a try.

Few more things about screen sharing. 1) The brightness issue (of always at max) with the DisplayPort connected iMac is solved because you set the target iMac brightness as if it were your only machine. (Now what to do with this new male-male DisplayPort cable ...) 2) Setting up screen sharing does require a keyboard/mouse connected to the target iMac. But once done, you can unplug the keyboard/mouse. Restarting the target iMac (via button on the back) makes it show up in the Finder sidebar under "Shared" items. Select it, then select Share Screen... button in upper right of Finder window, and you get the shared screen on your source Mac. Now you look at the shared screen and log in as normal.

Last- You do have to keep the shared screen up on your source Mac so your mouse has the range it needs. Play with this and you will understand.

Hi,

maybe you changed the behavior of the Function-keys accidentally.

Have you tried the keys with the 'Fn'-key ?

http://docs.info.apple.com/article.html?path=Mac/10.6/en/8763.html

Regards

Stefan

Maybe a SMC-reset http://support.apple.com/kb/HT3964 can help

Haven't had such problem myself yet.

You don't seem to be alone with it https://discussions.apple.com/thread/3138368?answerId=15515094022#15515094022

I posted this in the linked discussion thread above, but just in case it might help someone finding this thread:

I've futzed with this for a while using a MBP and an iMac, both running 10.6.8. The problem is inconsistent for me, but seems to be linked to how long I've had the iMac on. If on chronically (as I usually leave it), the iMac tends not to respond to F1/F2 brightness keystrokes when I connect my MBP and use the iMac in target display mode. But if I reboot the iMac and then connect from my already running MBP, this restores brightness keystroke response. That is:

1) With MBP and iMac running, connect mini DP to start target display mode on iMac

2) If brightness keystrokes don't respond, disconnect mini DP and reboot iMac, leave MBP running

3) After booted to desktop on the iMac, reconnect mini DP - brightness keys should respond

This has worked consistently for me. Hope it works for you, too. Hope Apple fixes this permanently somehow soon, it sure is annoying.

If you have a wired keyboard, plug that into the iMac and use the brightness keys to get your desired brightness. You can do this while the iMac is the second monitor. Worked for me.

I had the same problem with 10.6.8. But it works well with the mountion lion upgrade.

DUDE - you're a genius! Thanks for this, I've been squinting for the last month because of my bright iMac (aspecially at night) and I'm on deadline so HAVE to work all night...

Thank you thank you thank you!!!!

ONE MORE SUCCCESSFULL SOLUTION. I have iMac 27" with Mini DisplayPort used as an external monitor for Macbook Pro Retina 15" with Thunderbolt port connected with MDP cable. After the iMac system was automatically updated to version 10.6.8, the brightness stopped adjusting by pressing F1 and F2 keys on the wireless iMac keyboard during the connection. I've tried to reboot iMac in different special modes, reseting, etc..., but all the attempts failed. Finally I've remembered that I still have the original istallation disc with the older OS X version, that was provided with the iMac. I've used it to install OS X 10.6.4, and got all the brightness functions back, constatly working after each reboot. Of course, it would be better to have the same functions in the latest OS version, but now I'm quite happy to get the external monitor mode properly available again.

THANK YOU!!!! - finally a solution that WORKS!