I recently heard about duet, the app for iOS that allows an iPad or iPhone to be used as an extra display for macs -- and decided to give it a try. Plus, it would be nice to be able to re-purpose an old iPad for use as a second display.
Installing Duet Display is a two stage process. First the app needs installed on an iPad or iPhone, and a second app (also called duet) is required on the Mac to act as a video driver for the iOS device.
Stage one: Install Duet Display on an iPhone or iPad from the App Store.
Stage Two: After duet installs on your iPad or iPhone, download the Duet app for your Mac using the link provided by the iOS app:
The link provided in the instructions immediately starts a download after it is entered in a browser window, so please note you will not see a download page. So, be sure to monitor download progress:
Next, extract duet.app from the downloaded zip file and drag it to your Applications folder. Then open it as you would any other Mac application. After duet starts running, an icon appears on the top toolbar.
At this point, your Mac is now ready to use your iPad as a second screen, connected via lightning cable or the older style 30 pin connector cable.
For my test, I connected a 3rd Generation iPad running iOS 8.1.2 to a MacBook Pro with 2.9 GHz Intel i7 CPU, 8GB of RAM, running Mac OS X Yosemite version 10.10.1.
Before connecting an iPad to your Mac, start the duet iOS app, it should display a "Connect to Mac" message, followed by "Launching Duet" when plugged in the mac. Your mac will then "find" the second iPad screen.
Immediately after connecting though, I discovered a small annoyance: On my system, iPhoto launched shortly after my iPad was connected, even though I've had this behavior disabled for years.
To run duet through its paces, I decided to open various applications and move their windows back and forth between my normal Mac screen and iPad "screen." This usually worked OK; most of the time the app window would "plop" into place fine if quickly moved to the iPad screen. Scrolling, such as in a browser window, usually was fast and responsive with little or no lag.
But I then encountered multiple issues when I began positioning app windows across both Mac and iPad screens.
I can definitively say that duet is by no means a polished application. I found many quirks during testing. Testing duet gave me the impression that it was rushed to market in order to make it on the App Store for the holiday shopping season, released too early before all of its bugs were ironed out.
Most of the bugs I encountered with duet occurred when an app window "spanned" across mac and iPad screens. The screenshot below was taken on my iPad, after I positioned a Chrome browser window across the two screens.
At other times the spanning bug could produce random results: Sometimes a window would disappear entirely, as it did to a terminal window spanning both screens.
I discovered a temporary fix: Clicking either Cycle Through Windows or Bring All to Front options in Finder's Window menu usually brings hidden app windows "back to life."
In one odd case, my dock moved from the primary Mac screen to the iPad screen. I was able to restore its original position using System Preferences -- Dock, moving its position first to Left, then back to Bottom.
If you have a mac with a DVD player, then duet will likely disappoint. I tested three different DVD movies and could see only a gray video window using DVD Player on both mac and iPad screens. After I disconnected the iPad, I was again able to view movie content of each DVD on the mac screen with no issues.
However, I was able to use VLC successfully to view AVI files with duet -- video content appeared and displayed normally on both screens.
Not all about duet is bad, there are situations in which it can be handy. For instance, I tested a scenario using Dash to scroll through programming documentation on the iPad screen and running XCode, with its window in the larger mac screen:
So, duet can be useful, but it requires a willingness to put up with occasional odd quirks and bugs -- and knowing its limitations.
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