Use an iMac as a 
second monitor

Christopher Breen
28 August, 2011
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My wife is running an old iMac G5, and we’d like to move her to a MacBook Air. She sees my setup with a laptop and second monitor and wants to know if she can use her iMac as a second monitor.

- David Camp

In a way, yes, but you don’t do this by simply stringing a video cable between the two Macs. Rather, you use Patrick Stein’s US$29.90 ScreenRecycler, a VNC (Virtual Network Computing) tool that uses your network to place the image of one Mac’s display on the other’s display.

With the Macs on the same network, install ScreenRecycler on the MacBook Air (the Mac you want to project to the other Mac).

After installing the required driver and restarting the MacBook Air, launch ScreenRecycler.

On the iMac (the Mac you’ll use as the display), launch a VNC client (a trial copy of Stein’s $40 JollyFastVNC is included with Screen-Recycler).

The two Macs should automatically connect over Bonjour.

Open the MacBook Air’s Displays system preference. You should see two monitors represented – the MacBook Air’s display and the Screen-Recycler display (which appears within the VNC client window on the iMac).

You can now arrange the position of these displays by dragging the second one into the proper position (to the right of the main display if the iMac sits to the right of the MacBook Air, for example).

It’s likely that you’ll also have to adjust the resolution of the ScreenRecycler display. You do this within the Scr.Recycler1 window that appears on the MacBook Air’s screen.

Performance isn’t great, as there’s a lag between one computer and another – how brutal a lag depends on your network speed. The lag will produce artefacts on the iMac’s display when you move objects on its screen.

For this reason, I’d maintain the MacBook Air’s screen for objects that move a lot – say, windows that display movies or that you use for photo editing. The iMac can work as a place to throw program palettes or documents you want to read rather than extensively work with.

The alternative, of course, is to purchase an inexpensive second monitor. You’ll be happier with the results.

One Comment

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  1. Denis says:

    Or just use the built in screen sharing function, which is also based on the open source VNC.

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