My wife is running an old iMac G5, but she’d like a MacBook Air. She sees my setup with a laptop and second monitor and wants to know whether she could use her iMac as a second monitor.
David Camp

In a way, yes, but you can’t do this by simply stringing a video cable between the two. Rather, use Patrick Stein’s £19.53 ScreenRecycler (, a VNC (Virtual Network Computing) tool that uses your network to place the image of one Mac’s display on the other’s.

With the Macs on the same network, install ScreenRecycler on the Air (the Mac you want to project to the other). After installing the required driver and restarting the Air, launch ScreenRecycler. On the iMac (the Mac you’ll use as the display), launch a VNC client (a trial copy of Stein’s JollyFastVNC is included with Screen­Recycler). The two machines should automatically connect over Bonjour.

Open the MacBook Air’s Displays system preference. You should see two monitors represented – the MacBook Air’s and the Screen­Recycler screen (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 correct 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 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.

Use the Displays system preference to adjust the resolution settings of your Mac on the iMac’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 artifacts on the iMac’s display when you move objects on its screen. For this reason, we’d maintain the MacBook Air’s display for objects that move a lot – for example, windows that display movies. The iMac can then 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 probably be happier with the results.