Q: How can I use the built-in Isight camera with an external camera (usb/firewire) at the same time?

Simple question with a not so simple answer.

(a) If you mean that you want to run multiple apps simultaneously using a different camera with each app, you may encounter computing power limitations.  Digital video is processor intensive.  The only way to know if your Mac can do this it to try it.  If the video does not work together but each app works when it it the only app running, you are likely overloading your Mac's ability to process and/or move all the required data in your data bus.  You can get a better indication of whether this is the case by watching your Activity Monitor utility while running the apps you want to use.

(b) If you mean that you want to have more than one compatible camera connected to your Mac simultaneously for ease of changing between video sources, some, but not necessarily all, apps you are using to operate your camera(s) allow you to select between your cameras.

How you select among connected cameras depends on which application you are using. Here is how camera selection works in a few examples:

(1) For iChat, you can choose which iSight you use in the "Camera:" choices bar in iChat > Preferences... > Audio/Video that appears when more than one compatible camera is connected. Although your camera choices will be different, the choices bar will look something similar to the Preferences settings shown here:

If you cannot see the "Camera" choices bar, your Mac is recognizing only one (or none) of your cameras. In that case, consider the suggestions fromhttp://support.apple.com/kb/HT2090 for iSight problems or refer to your other camera's documentation for help.

This particular choices bar solution applies ONLY to iChat. Most other applications also have settings that allow you to choose which camera to use. However, they do not all work the same way.

(2) For instance, iMovie HD's camera choice is NOT set via Preferences. When you have more than one compatible camera connected, iMovie6 HD uses a drop-down menu choice something like this (depending on which version of iMovie you use):

Note: Because I had no built-in iSight connected when I made this example, and because my external iSight was not connected, the drop-down menu showed only "Time Lapse." Because your Mac has a built-in iSight, your built-in iSight would show in the drop-down menu even when no other camera is connected. Connecting an additional Mac compatible webcam should allow you to choose either camera.

Other iMovie versions work slightly differently.

iMovie 9 (from iLife '11) uses a different camera choice button shown in this article:

  http://docs.info.apple.com/article.html?path=iMovie/9.0/en/mov39f84285.html

iMovie 8 (from iLife '09) is slightly different as explained in this article:

  http://docs.info.apple.com/article.html?path=iMovie/8.0/en/10172.html

In general, you can use your Mac's help for the application in use to find out how to select among more than one connected camera.

(3) Photo Booth in Snow Leopard 10.6.x and later uses the Photo Booth > Camera menu command to select which camera to use.

Note for readers with older Mac OS X: The previous version of Photo Booth that came with Tiger (10.4.x) is such a simple, basic app that it offers no menu selectable choice. Unless your built-in iSight is already occupied as the camera being used by some open application before you launch Photo Booth, Photo Booth will use ONLY your built-in iSight.

However, you can use the trick from ¶ 4 of http://docs.info.apple.com/article.html?artnum=302781 to let Photo Booth use an external camera.

(If you have an external Firewire camera connected, it may be used in preference to any USB webcam. If that is a problem for you, merely disconnect the problem Firewire device.)

(4) For FaceTime, launch the app and click the Video menu item.

If your Mac recognizes more than one connected compatible camera, a "Camera" section listing the cameras from which you can choose will appear there. Clicking on the desired camera name will let you select the one you want as shown in this image from my Mac Pro and LED Cinema Display:

If your Mac recognizes only one compatible camera, the "Camera" section will not appear in the Video menu, but FaceTime will automatically use the connected camera that is recognized by OS X.

(5) I do not use Skype oir Oovoo.  For those or other apps, see Help for each app for info on how to select your desired camera.

Message was edited by: EZ Jim