OS X 10.5 and 10.6 both have the robust Screen Sharing program built in. It lets you access other 10.5 and 10.6 systems, and it’s backward-compatible with the industry-standard VNC (virtual network computing) protocol. Unfortunately, on its own, that program alone isn’t very good at reaching out over the Internet; it’s best for connecting to computers that are hooked up to the same router, using Bonjour.
Paired with Back to My Mac, though, Screen Sharing becomes much more powerful—as long as the machines you want to connect with are all under your personal control. That’s because Back to My Mac requires a MobileMe account, and each computer you want to use must be logged into the same account.
In addition to being built into OS X, Screen Sharing manages multiple monitors relatively well. It's also relatively speedy and simple to set up. If you enable File Sharing on the remote system, you can transfer files over the same connection.
The biggest disadvantage of OS X’s built in tools are that they require a MobileMe subscription. Back to My Mac can also be picky about the routers it will work with. Also, unlike some other remote-access options, they don’t allow you to select a lower color bit-depth for the remote screen (which requires less bandwidth); you can, however, enable lossy compression, which can reduce both the bandwidth required and the quality of the screen image.
Assuming you have such an account, you enable Back to My Mac in the MobileMe preference pane. On that pane’s Back to My Mac tab, you click Start to activate the service; a green dot appears when it has successfully registered your computer with the MobileMe servers. On the systems you want to remotely access, you also need to turn on Screen Sharing in the Sharing preference pane.
Once active, any remote computers registered to the same MobileMe account should appear in the Shared section of the Finder sidebar. The Finder combines computers available via Bonjour on the local network and via Back to My Mac over the Internet in the same list. If you travel, that can be both reassuring and a little confusing.
To access one of those computers, select it from the Sidebar list, then click the Share Screen button. (That button is in the upper right of Finder windows in all but the Column view; in the latter, it’s below the computer icon). You should then be able to control the remote system’s screen. If you don’t see Share Screen as an option, the screen-sharing service isn’t on in the remote system or there’s a network problem.
Once you click Share Screen, the Screen Sharing program launches and a connection is attempted. If the remote system has the same OS X user name and password as the computer from which you’re connecting, you may not be prompted to login. In all other cases, you should be asked for a valid user name and password for the remote machine. (You can choose to store them in the Keychain for future connections; you should.)
With a successful session open, you have only a handful of options available.
Scaling You can shrink a remote screen (or set of screens) to fit the open sharing window by selecting View > Turn Scaling On, or by clicking the scaling button in the Screen Sharing toolbar.
Quality You can conserve bandwidth by choosing View > Adaptive Quality. This enables lossy compression, which may pixelate the screen image, depending on the speed of your connection is and the frequency of updates. The alternative, Full Quality, uses much more bandwidth, but preserves fidelity.
Monitors If the remote system has two more monitors attached, you can use the View menu or a pop-up on the toolbar to choose whether to see a single monitor at a time or all monitors.
Send or receive Clipboard The Edit -> Get Clipboard and Edit -> Send Clipboard options let you exchange the contents of the local and remote clipboards.
Snow Leopard’s version of Screen Sharing improved on Leopard’s by capturing all keystrokes as part of your remote session; in Leopard, pressing Command-Tab would cycle programs on the local computer, not the one you were viewing remotely.
If Back to My Mac isn’t working for you, open the Back to My Mac tab in the MobileMe preference pane. If you see a green dot for connection status, click Stop, wait a moment, and click Start again. This often clears up problems. (Clicking Stop will disconnect any mounted drives or other remote network shares that are using Back to My Mac.) If you see a yellow or red dot, consult our troubleshooting article or Apple’s.
Updated 10:50 PT 7/19/10 to clarify statement regarding multiple monitor support.