Screen Sharing from Macbook 12" to iMac

My Macbook sharing its screen with my iMac. Sharing is caring.

I recently got a new Macbook 12" to replace my almost 5 year old Macbook Air 13". I’m very happy with this decision. I carry my laptop with me a lot so I’m over the moon to have a retina screen in such a small, light body.

When I’m not working on the go I work from my living room. There I have an iMac 21.5" I got a while back to act as display. I find 24" displays to be too large and I like having a backup computer, but those are topics for another day.

Previously with my Macbook Air I used Target Display Mode and a thunderbolt cable to use the iMac as a display. As far as I can figure there is no way to use Target Display Mode to duplicate this setup for the new Macbook 12".

Let’s look at the system requirements for using Target Display Mode:

System Requirements for Target Display Mode

It looks to me like if you don’t have a thunderbolt port on your “other Mac” you are out of luck. But maybe they just haven’t updated this page since the Macbook 12" came out.

I should probably have mentioned by now that the Macbook 12" does not have a thunderbolt port; it only has one port: USB-C. I picked up the USB-C Digital AV Multiport Adapter to connect to an external HDMI display. Surely I can use that to connect to the iMac? Let’s look at the what it can do:

Information on the USB-C Digital AV Multiport Adapter

Great it can connect to external HDMI displays. It seems reasonable to me that HDMI to thunderbolt could be an answer but this spec for Apple displays leaves me with doubts:

System Requirements for Apple Displays

Mind you I didn’t go out and buy an cables to test that they don’t work. I’ve tried to use a mini display port cable in place of a thunderbolt cable before, and now I trust that Apple means it when they say you need a thunderbolt port on your “other Mac” and never even mention HDMI.

So I packed up my iMac and put it in the closet while I considered selling it and buying Dell monitor. Then I procrastinated doing anything about it.

After a couple weeks I missed having a larger screen so I pulled out the larger screen I already owned: the iMac. I did a couple of internet searches looking for the latest and greatest way to turn my iMac into an Airplay Display. My favorite solutions to computer problems are the ones that don’t require me to install any new software or buy anything, so when I came across Screen Sharing.app that has shipped with OSX since 10.4 I immediately knew which solution I was going to try first.

On my Macbook I opened up System Preferences > Sharing, checked the box for Screen Sharing, and took note of the VNC address: vnc://10.0.1.48/.

Then on my iMac I opened up Screen Sharing.app and entered the VNC address.

After pressing Connect I entered the username and password for my user on my Macbook and pressed Connect again.

And voila! There was my Macbook screen on my iMac. The quality was poor so I looked around a selected View > Full Quality. Also it wasn’t taking up the whole screen on my iMac. To get a better fullscreen effect I lowered the display resolution on my iMac. There are still some small black bars on the sides but the screen now takes up 100% of the height.

I am happy with this solution’s simplicity. I also super enjoy that the display resolution on my Macbook does not change. I always find that super annoying when using an external display. I keep my apps tidy (shout out to SizeUp.app). I put this here and that there because thats where I want them to be. I do not want them to shift when I plug in and unplug my laptop to an external display. Now they don’t!

Lag is an issue with this solution, but it would be improved by the addition of some ethernet cables instead of relying on wifi (my video calls would benefit from this too). Don’t worry my USB-C Digital AV Multiport Adapter has a USB port and I have a USB to Ethernet adapter.

Another caveat is that unless I am using its keyboard or mouse my iMac will fall asleep even if my Macbook is still awake. This is easily solved by using Caffeine.app on my iMac, which I have used and loved for years. I could also adjust my System Preferences > Energy Saver settings.

Aren’t computers wonderful/terrible? Ok, I think I’ll get back to work now.